Spec tests don't need simd flag anymore

SIMD is now shipped, so we don't need to pass the experimental wasm simd
flag.

Change-Id: I54090cec575da5eecfd2bf9a455ac5d0ef3f146e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3169313
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76918}

test/wasm-spec-tests/testcfg.py

@@ -17,11 +17,6 @@ proposal_flags = [{
                     'flags': ['--experimental-wasm-return-call',
                               '--wasm-staging']
                   },
-                  {
-                    'name': 'simd',
-                    'flags': ['--experimental-wasm-simd',
-                              '--wasm-staging']
-                  },
                   {
                     'name': 'memory64',
                     'flags': ['--experimental-wasm-memory64',