Change how unused function parameters are handled

[leekillough]

This changes the UNUSED() macro to be used within the body of a function rather than inside its declaration

• It avoids cluttering the function declaration, which is visually distracting and might complicate doc generation tools
• It emphasizes that the parameter being unused is an implementation detail of the function and not a part of its interface
• It is used within the body of a function with a syntax which makes it clear that it should not be used in a function declaration
• The old UNUSED() macro added attributes to parameters; the new UNUSED() macro casts a parameter to void to hide the unused parameter warning
• The old UNUSED() macro was used in some function declarations without definitions, where it had no effect; these have been removed
• The new UNUSED() macro appears at the beginning of a function definition and "declares" that a parameter is unused
• -Werror=unused-parameter is added to builds so that unused parameters not marked with UNUSED() are errors rather than warnings
• It fixes one unused parameter in rng.h which was not marked UNUSED()
• Except for a couple of places, which had unused parameter packs or had commented-out function declarations with UNUSED() in them, this was all automatically done by a script (attached), which can be run on other codes-in-progress

[github-actions]

CLANG-FORMAT TEST - FAILED (on last commit):
Run > ./scripts/clang-format-test.sh using clang-format v12 to check formatting

[github-actions]

CMAKE-FORMAT TEST - PASSED

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CLANG-FORMAT TEST - PASSED

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[sst-autotester]

Status Flag 'Pre-Test Inspection' - - This Pull Request Requires Inspection... The code must be inspected by a member of the Team before Testing/Merging
NO INSPECTION HAS BEEN PERFORMED ON THIS PULL REQUEST! - This PR must be inspected by setting label 'AT: PRE-TEST INSPECTED'.

[github-actions]

CLANG-FORMAT TEST - FAILED (on last commit):
Run > ./scripts/clang-format-test.sh using clang-format v12 to check formatting

[github-actions]

CMAKE-FORMAT TEST - PASSED

[sst-autotester]

Status Flag 'Pre-Test Inspection' - - This Pull Request Requires Inspection... The code must be inspected by a member of the Team before Testing/Merging
NO INSPECTION HAS BEEN PERFORMED ON THIS PULL REQUEST! - This PR must be inspected by setting label 'AT: PRE-TEST INSPECTED'.