[CMake] sanitizer is forced to "address sanitizer"

In fuzzing mode or compatibility mode, address sanitizer is forced.
https://github.com/google/fuzztest/blob/a990537097b6fd337436f7662fb39fc91fa01f3f/cmake/FuzzTestFlagSetup.cmake#L2-L3

This is problematic on oss-fuzz which has different sanitizers. We therefore remove those flags https://github.com/AOMediaCodec/libavif/blob/d074bae4b0b1d7423d102f6d9d5e0c5303971a51/ext/fuzztest.cmd#L14 and use the ones set in the environment variable `CXXFLAGS` by oss-fuzz.

I believe those sanitizer flags should only be set for `FUZZTEST_FUZZING_MODE`, not when `FUZZTEST_COMPATIBILITY_MODE STREQUAL "libfuzzer")`.