[clang] [analyzer] Remove impossible BugType from CStringChecker (PR #152163)

[Donát Nagy via cfe-commits]

NagyDonat wrote:

Rerunning the CI checks didn't change the fact that the Github automation runs the tests on a merge between my commit (which would pass the CI) with 74af2cec7bbd307d1dcb7f9f3cdf339d551a1f9f (where the CI fails) instead of a more recent main revision (where the CI would pass). I did a merge from main to force the use of a non-broken revision.

https://github.com/llvm/llvm-project/pull/152163