[fuzzer][afl] Remove AFL_DRIVER_EXTRA_STATS_FILENAME

Summary:
Remove this feature as it is unused, buggy, and not worth correcting
since the forkserver makes it difficult.

Reviewers: morehouse, jfb

Reviewed By: morehouse

Differential Revision: https://reviews.llvm.org/D57308

llvm-svn: 352392
GitOrigin-RevId: 3720e2b39e4be7db2a62ff4447502e61f3681b59
1 file changed