[ctxprof][nfc] Remove redundant `SANITIZER_NO_THREAD_SAFETY_ANALYSIS` (#133784)
With the refactoring in PR #133744, `__llvm_ctx_profile_start_context` doesn't need to be marked `SANITIZER_NO_THREAD_SAFETY_ANALYSIS` because `tryStartContextGivenRoot` (where the bulk of the logic went) is.