[std.meta] Remove unnecessary T/alias T overloads

Reboot of dlang#7513.
Alias parameters accept basic types and #22393 is finally fixed now.
Update Alias, Replace and ReplaceAll, isSame.
Remove OldAlias, GenericReplace.
Also use alias parameters instead of variadic for `isLessEq`.

Author: ntrel

std/meta.d

@@ -175,9 +175,6 @@ alias AliasSeq(TList...) = TList;
  */
 alias Alias(alias a) = a;
 
-/// Ditto
-alias Alias(T) = T;
-
 ///
 @safe unittest
 {
@@ -222,32 +219,6 @@ alias Alias(T) = T;
     assert(g == 7);
 }
 
-package template OldAlias(alias a)
-{
-    static if (__traits(compiles, { alias x = a; }))
-        alias OldAlias = a;
-    else static if (__traits(compiles, { enum x = a; }))
-        enum OldAlias = a;
-    else
-        static assert(0, "Cannot alias " ~ a.stringof);
-}
-
-package template OldAlias(T)
-if (!isAggregateType!T || is(Unqual!T == T))
-{
-    alias OldAlias = T;
-}
-
-@safe unittest
-{
-    static struct Foo {}
-    //static assert(is(OldAlias!(const(Foo)) == const Foo));
-    static assert(is(OldAlias!(const(int)) == const(int)));
-    static assert(OldAlias!123 == 123);
-    enum abc = 123;
-    static assert(OldAlias!abc == 123);
-}
-
 /**
  * Returns the index of the first occurrence of `args[0]` in the
  * sequence `args[1 .. $]`. `args` may be types or compile-time values.
@@ -431,30 +402,26 @@ template NoDuplicates(args...)
 
 
 /**
- * Returns an `AliasSeq` created from TList with the first occurrence
+ * Returns an `AliasSeq` created from Seq with the first occurrence
  * of T, if found, replaced with U.
  */
-template Replace(T, U, TList...)
-{
-    alias Replace = GenericReplace!(T, U, TList).result;
-}
-
-/// Ditto
-template Replace(alias T, U, TList...)
+template Replace(alias T, alias U, Seq...)
 {
-    alias Replace = GenericReplace!(T, U, TList).result;
-}
-
-/// Ditto
-template Replace(T, alias U, TList...)
-{
-    alias Replace = GenericReplace!(T, U, TList).result;
-}
+    static if (Seq.length)
+    {
+        alias head = Seq[0 .. 1];
+        alias tail = Seq[1 .. $];
 
-/// Ditto
-template Replace(alias T, alias U, TList...)
-{
-    alias Replace = GenericReplace!(T, U, TList).result;
+        static if (isSame!(T, head))
+            alias Replace = AliasSeq!(U, tail);
+        else
+            alias Replace = AliasSeq!(head,
+                Replace!(T, U, tail));
+    }
+    else
+    {
+        alias Replace = AliasSeq!();
+    }
 }
 
 ///
@@ -466,31 +433,6 @@ template Replace(alias T, alias U, TList...)
     static assert(is(TL == AliasSeq!(int, char, long, int, float)));
 }
 
-// [internal]
-private template GenericReplace(args...)
-if (args.length >= 2)
-{
-    alias from  = OldAlias!(args[0]);
-    alias to    = OldAlias!(args[1]);
-    alias tuple = args[2 .. $];
-
-    static if (tuple.length)
-    {
-        alias head = OldAlias!(tuple[0]);
-        alias tail = tuple[1 .. $];
-
-        static if (isSame!(from, head))
-            alias result = AliasSeq!(to, tail);
-        else
-            alias result = AliasSeq!(head,
-                GenericReplace!(from, to, tail).result);
-    }
-    else
-    {
-        alias result = AliasSeq!();
-    }
- }
-
 @safe unittest
 {
     static assert(Pack!(Replace!(byte, ubyte,
@@ -511,16 +453,16 @@ if (args.length >= 2)
 }
 
 /**
- * Returns an `AliasSeq` created from `args[2 .. $]` with all occurrences
- * of `args[0]`, if any, replaced with `args[1]`.
+ * Returns an `AliasSeq` created from args with all occurrences
+ * of T, if found, replaced with U.
  */
-template ReplaceAll(args...)
+template ReplaceAll(alias T, alias U, args...)
 {
     alias ReplaceAll = AliasSeq!();
-    static foreach (arg; args[2 .. $])
+    static foreach (arg; args)
     {
-        static if (isSame!(args[0], arg))
-            ReplaceAll = AliasSeq!(ReplaceAll, args[1]);
+        static if (isSame!(T, arg))
+            ReplaceAll = AliasSeq!(ReplaceAll, U);
         else
             ReplaceAll = AliasSeq!(ReplaceAll, arg);
     }
@@ -1297,10 +1239,9 @@ private template staticMerge(alias cmp, uint mid, items...)
             staticMerge!(cmp, mid - run, items[run .. mid], items[mid + 1 .. $]));
 }
 
-private template isLessEq(alias cmp, Seq...)
-if (Seq.length == 2)
+private template isLessEq(alias cmp, alias A, alias B)
 {
-    private enum Result = cmp!(Seq[1], Seq[0]);
+    private enum Result = cmp!(B, A);
     static if (is(typeof(Result) == bool))
         enum isLessEq = !Result;
     else static if (is(typeof(Result) : int))
@@ -1452,11 +1393,6 @@ private template isSame(alias a, alias b)
         enum isSame = __traits(isSame, a, b);
     }
 }
-// TODO: remove after https://github.com/dlang/dmd/pull/11320 and https://issues.dlang.org/show_bug.cgi?id=21889 are fixed
-private template isSame(A, B)
-{
-    enum isSame = is(A == B);
-}
 
 @safe unittest
 {