The compile step that cranelift-fuzzgen does also triggers IR
verification. So all bugs that cranelift-fuzzgen-verify could catch are
also caught by cranelift-fuzzgen. Removing redundant fuzzers lets us
spend limited fuzz-testing CPU time budgets better.
`wasm-smith` v0.11 has support for generating shared memories when the
`threads_enabled` configuration flag is set. This change turns on that
flag occasionally. This also upgrades `wasm-smith` to v0.11.1 to always
generate shared memory with a known maximum.
