[clang] [OpenMP] Remove complex reduction variable support (PR #82497)

[Akash Banerjee via cfe-commits]

TIFitis wrote:

@alexey-bataev I'm facing issues adding the test to Clang tests as it uses the complex.h header files. From what I can tell header files don't seem to be supported. Is there any way to add the test you provided to the Clang tests or a different one which can still check for the complex case?

https://github.com/llvm/llvm-project/pull/82497