[clang] [clang-repl] Don't double-remove extern "C" decls from the IdResolver (PR #218129)

[via cfe-commits]

llvmbot wrote:

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Failed to cherry-pick: d09e5d23aeddabc7549b1355777caea1214b40c6

https://github.com/llvm/llvm-project/actions/runs/32628545433

Please manually backport the fix and push it to your github fork.  Once this is done, please create a [pull request](https://github.com/llvm/llvm-project/compare)

https://github.com/llvm/llvm-project/pull/218129