[scripts] Update name of experimental Wasm V8 flags

[Liedtke]

These flags got renamed in https://crrev.com/c/8426472.

Note that this is just the code change, I don't know if there is any pipeline in place to automatically update the ClusterFuzz fuzzer.

[stevenfontanella]

@Liedtke can you run fuzz_opt.py as a sanity check?

Also I guess this would break the fuzzer with earlier versions of V8 that don't have the renamed flags. Is that fine @kripken? I get the impression that we don't care that much about backward compatibility with earlier versions of V8 for fuzzing.

[kripken]

Yes, we don't care about older V8 - we just expect people to update their V8.

[stevenfontanella]

LGTM if scripts/fuzz_opt.py runs successfully for a few iterations.