Temporarily disable SIMD fuzzing on CI (#3376)

We've got a large crop of fuzz-bugs from fuzzing with enabled-with-SIMD
on oss-fuzz but at this point the fuzz stats from oss-fuzz say that the
fuzzers like v8 are 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.

crates/fuzzing/src/generators.rs

@@ -142,12 +142,6 @@ impl wasm_smith::Config for WasmtimeDefaultConfig {
         4
     }
 
-    // Turn some wasm features default-on for those that have a finished
-    // implementation in Wasmtime.
-    fn simd_enabled(&self) -> bool {
-        true
-    }
-
     fn reference_types_enabled(&self) -> bool {
         true
     }

crates/fuzzing/src/lib.rs

@@ -40,7 +40,6 @@ pub fn fuzz_default_config(strategy: wasmtime::Strategy) -> anyhow::Result<wasmt
         .wasm_reference_types(true)
         .wasm_module_linking(true)
         .wasm_multi_memory(true)
-        .wasm_simd(true)
         .wasm_memory64(true)
         .strategy(strategy)?;
     Ok(config)

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);