[wasm] Remove --wasm-atomics-on-non-shared-memory flag

The flag has been enabled by default for two version now, so it is time
to remove it.

R=binji@chromium.org

Bug: v8:9921
Change-Id: I833e04a3f9d238e7bcf27e93148c9492776af3c6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2402034Reviewed-by: Ben Smith <binji@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70838}

src/flags/flag-definitions.h

@@ -892,10 +892,6 @@ DEFINE_DEBUG_BOOL(trace_wasm_lazy_compilation, false,
 DEFINE_BOOL(wasm_lazy_validation, false,
             "enable lazy validation for lazily compiled wasm functions")
 
-// Flags for wasm prototyping that are not strictly features i.e., part of
-// an existing proposal that may be conditionally enabled.
-DEFINE_BOOL(wasm_atomics_on_non_shared_memory, true,
-            "allow atomic operations on non-shared WebAssembly memory")
 DEFINE_BOOL(wasm_grow_shared_memory, true,
             "allow growing shared WebAssembly memory objects")
 DEFINE_BOOL(wasm_simd_post_mvp, false,

src/wasm/function-body-decoder-impl.h

@@ -2181,7 +2181,7 @@ class WasmFullDecoder : public WasmDecoder<validate> {
   }
 
   bool CheckHasMemoryForAtomics() {
-    if (FLAG_wasm_atomics_on_non_shared_memory && CheckHasMemory()) return true;
+    if (CheckHasMemory()) return true;
     if (!VALIDATE(this->module_->has_shared_memory)) {
       this->DecodeError(this->pc_ - 1,
                         "Atomic opcodes used without shared memory");

test/mjsunit/wasm/atomics-non-shared.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --experimental-wasm-threads --wasm-atomics-on-non-shared-memory
+// Flags: --experimental-wasm-threads
 
 load("test/mjsunit/wasm/wasm-module-builder.js");