Temporarily disable SIMD fuzzing with v8 on CI

We've got a large crop of fuzz-bugs from fuzzing with
v8-enabled-with-SIMD on CI but at this point the fuzz stats from
oss-fuzz say that the fuzzer is spending less than 50% of its time
actually fuzzing and presumably mostly hitting crashes and such. While
we fix the other issues this disables simd for fuzzing with v8 so we can
try to see if we can weed out other issues.

Author: alexcrichton

fuzz/fuzz_targets/differential_v8.rs

@@ -5,7 +5,7 @@ use wasmtime_fuzzing::{generators, oracles};
 
 fuzz_target!(|data: (
     generators::Config,
-    wasm_smith::ConfiguredModule<oracles::SingleFunctionModuleConfig<true, true>>
+    wasm_smith::ConfiguredModule<oracles::SingleFunctionModuleConfig<false, true>>
 )| {
     let (config, mut wasm) = data;
     wasm.module.ensure_termination(1000);