[llvm] [Bazel] Remove redundant gtest_main from codegen_tests, codegen_globalisel_tests, mi_tests (PR #135316)

[Keith Smiley via llvm-commits]

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

Lgtm. Seems like maybe these tests should toss the main and move initLLVM into a test setup function 

https://github.com/llvm/llvm-project/pull/135316