Remove Unused RTLSYMs from DMD

[nybzmr]

This PR removes several unused RTLSYMs that became obsolete due to past backend refactorings (mainly from translation PRs by @teodutu). These symbols were previously used in e2ir.d, but their references have been removed, making them redundant.
✔️ Cleaned up rtlsym.d, drtlsym.d, e2ir.d mappings and other related files.
✔️ Ensured that tracing GC hooks (toTraceGC) are updated accordingly.

@teodutu @dlang/compiler-team

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

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[dkorpel]

This 25 can be lowered to 9, or completely removed

[nybzmr]

Thanks for the suggestion! I'll check how many elements are actually used and update the size accordingly. If it's possible to remove the explicit size altogether, I'll do that as well.