Don't take rustc-literal-escaper from sysroot

This resulted in the following error for me:

    error[E0464]: multiple candidates for `rlib` dependency `rustc_literal_escaper` found
      --> clippy_dev/src/lib.rs:25:1
       |
    25 | extern crate rustc_literal_escaper;
       | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       |
       = note: candidate #1: /home/pkrones/.rustup/toolchains/nightly-2025-12-25-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_literal_escaper-4f30574e01c3dad1.rlib
       = note: candidate rust-lang#2: /home/pkrones/.rustup/toolchains/nightly-2025-12-25-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_literal_escaper-c8a0e29ad1040cee.rmeta

Other tools in the Rust repo also take that as an explicit dependency, like rust-analyzer or lint-docs.

Author: flip1995

clippy_dev/Cargo.toml

@@ -10,6 +10,7 @@ clap = { version = "4.4", features = ["derive"] }
 indoc = "1.0"
 itertools = "0.12"
 opener = "0.7"
+rustc-literal-escaper = "0.0.5"
 walkdir = "2.3"
 
 [package.metadata.rust-analyzer]

clippy_dev/src/lib.rs

@@ -22,7 +22,6 @@ extern crate rustc_arena;
 #[expect(unused_extern_crates, reason = "required to link to rustc crates")]
 extern crate rustc_driver;
 extern crate rustc_lexer;
-extern crate rustc_literal_escaper;
 
 pub mod deprecate_lint;
 pub mod dogfood;