Don't include libarchive fuzz tests by default

These tests are basic fuzz tests that permute input to trigger crashes
rather than regression or unit tests. Additionally, some of them take a
rather long time to run and should probably be run on a dedicated fuzzing
job instead. Moreover, these simple tests use rand() instead of a real
fuzzing tool that generates interesting inputs (e.g. LLVM libFuzzer) so are
unlikely to find anything interesting when run in CI.

This allows removing one BROKEN_TESTS case due to timeouts and speeds up
running tests on emulated platforms such as QEMU.

Reviewed By: lwhsu, mm
Differential Revision: https://reviews.freebsd.org/D27153