[wasm] Remove unused --assume-asmjs-origin flag

This flag has no uses in any tests, and it's hard to image a use case
for debugging or similar.

R=ahaas@chromium.org

Bug: v8:10933
Change-Id: I2e96187e4410805824d213e9a9df152b54dd3fb2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2421825Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70052}

src/flags/flag-definitions.h

@@ -754,8 +754,6 @@ DEFINE_BOOL(untrusted_code_mitigations, V8_DEFAULT_UNTRUSTED_CODE_MITIGATIONS,
 DEFINE_BOOL(wasm_generic_wrapper, false,
             "use generic js-to-wasm wrapper instead of per-signature wrappers")
 DEFINE_BOOL(expose_wasm, true, "expose wasm interface to JavaScript")
-DEFINE_BOOL(assume_asmjs_origin, false,
-            "force wasm decoder to assume input is internal asm-wasm format")
 DEFINE_INT(wasm_num_compilation_tasks, 128,
            "maximum number of parallel compilation tasks for wasm")
 DEFINE_DEBUG_BOOL(trace_wasm_native_heap, false,

src/wasm/module-decoder.cc

@@ -295,13 +295,13 @@ class ModuleDecoderImpl : public Decoder {
   explicit ModuleDecoderImpl(const WasmFeatures& enabled, ModuleOrigin origin)
       : Decoder(nullptr, nullptr),
         enabled_features_(enabled),
-        origin_(FLAG_assume_asmjs_origin ? kAsmJsSloppyOrigin : origin) {}
+        origin_(origin) {}
 
   ModuleDecoderImpl(const WasmFeatures& enabled, const byte* module_start,
                     const byte* module_end, ModuleOrigin origin)
       : Decoder(module_start, module_end),
         enabled_features_(enabled),
-        origin_(FLAG_assume_asmjs_origin ? kAsmJsSloppyOrigin : origin) {
+        origin_(origin) {
     if (end_ < start_) {
       error(start_, "end is less than start");
       end_ = start_;