The gcov-based CoverageFuzz script was introduced in 8b6f1c4353836bae6aa683cbc65251165bd031ba, as a CMake's replacement for the legacy cov_fuzz target. However, neither cov_fuzz nor CoverageFuzz has a documented usage.
Instead, #32206 documented compiling for fuzz coverage using the LLVM/Clang toolchain, which does not involve the CoverageFuzz script.
This PR removes the never-documented CoverageFuzz script, which is likely unused.