Fuzztest, and the earlier libfuzzer, use SanitizerCoverage to understand what portions of the codebase they have explored. This system is very lightweight, and doesn't write to disk.

Currently, we set fcoverage-mapping and fprofile-instr-generate. This writes large amounts of data, and can exhaust storage. They also do not contribute to the fuzzers' operation.

We should remove these coverage systems, and use only SantizerCoverage.