[libFuzzer] remove the experimental support for clang coverage instrumentation. This mode has not been used and our experiments with https://github.com/google/fuzzer-test-suite show that this signal is weaker than the SanitizerCoverage

llvm-svn: 332034
GitOrigin-RevId: 59bf1e8b368c70f086cdb9a1df34ef9a0c72e062
8 files changed