[clang] [clang][analyzer] Remove 'alpha.core.CallAndMessageUnInitRefArg' from documentation (NFC). (PR #81138)

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https://github.com/NagyDonat approved this pull request.

This seems to be a fragment of the checker [core.CallAndMessage](https://clang.llvm.org/docs/analyzer/checkers.html#core-callandmessage-c-c-objc); I'd guess that it was separated from the other parts because it was more unstable than the rest.

Note that the documentation intro paragraph is apparently copypasted from the full `core.CallAndMessage` (even though it doesn't fit this special case).

Thanks for noticing and removing this obsolete documentation fragment.

https://github.com/llvm/llvm-project/pull/81138