linux/keg_relocate: clean up GCC RPATH fix.

[carlocab]

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There are no more formulae in Homebrew/core that have a runtime
dependency on GCC (see Homebrew/homebrew-core#110883), so there is no
more need to retain linkage with GCC through a versioned path.

[BrewTestBot]

Review period will end on 2022-09-22 at 16:58:10 UTC.

[BrewTestBot]

Review period skipped due to critical label.