Fix fuzzer builds.

- Updates the fuzzer builds to use SANITIZE_TARGET='fuzzer' instead of
'coverage'.
- Removed an old dependency that made fuzzer builds without ASan
an error.
- Fixed up the build flags to allow fuzzers to be built. Previously, the
coverage flags were manually provided. As the toolchain has moved on,
these flags are no longer compatible with libFuzzer, and so I've updated
them to use the correct, compatible flags.

Bug: 121042685
Test: With all patches in the bug merged, build a fuzzer using
'SANITIZE_TARGET=fuzzer mmma <your_fuzzer>'.

Change-Id: I86e6a26d27c22b3622cf6ea8760f502f607df6f0