[FP16] Disable float 16 fuzzing for now. (#6822)

Author: brendandahl

scripts/fuzz_opt.py

@@ -294,6 +294,8 @@ def is_git_repo():
 
 
 INITIAL_CONTENTS_IGNORE = [
+    # Float16 is still experimental.
+    'f16.wast',
     # not all relaxed SIMD instructions are implemented in the interpreter
     'relaxed-simd.wast',
     # TODO: fuzzer and interpreter support for strings