Prevent Fuzzilli from generating async arrow functions during mutation

Summary:
Hermes currently does not support async arrow functions, so let's prevent `AsyncArrowFunctionGenerator` from being selected by the `CodeGenMutator`

```test.js

async function asyncFunction() {
  console.log('test');
}

(async () => {
    console.log(await asyncFunction());
})();
```

```./hermes test.js
test.js:5:2: error: async functions are unsupported
(async () => {
 ^~~~~~~~~~~~~
Emitted 1 errors. exiting.
```

Differential Revision: D39601546

fbshipit-source-id: 120ae9ebdc1a9552ae2a034592b8af302dc07716

tools/fuzzers/fuzzilli/profile/HermesProfile.swift

@@ -28,7 +28,7 @@ let hermesProfile = Profile(
 
     additionalProgramTemplates: WeightedList<ProgramTemplate>([]),
 
-    disabledCodeGenerators: ["AsyncGeneratorFunctionGenerator", "ClassGenerator", "WithStatementGenerator"],
+    disabledCodeGenerators: ["AsyncArrowFunctionGenerator", "AsyncGeneratorFunctionGenerator", "ClassGenerator", "WithStatementGenerator"],
 
     additionalBuiltins: [
         "gc"                : .function([] => .undefined),