fuzz: remove fork-fuzzing scaffolding

fuzz: remove fork-fuzzing scaffolding

Fork-fuzzing provides a few pros, but our implementation prevents us
from using fuzzers other than libFuzzer, and may be causing issues such
as coverage-failure builds on OSS-Fuzz. It is not a great long-term
solution as it depends on internal implementation details of libFuzzer
(which is no longer in active development). Remove it in favor of other
methods of resetting state between inputs.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>