Revert "Reland^2 "[wasm] Enable Liftoff by default on ia32 and x64""

This reverts commit d8281a29.

Reason for revert: breaks win32: https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Win32/14559

Original change's description:
> Reland^2 "[wasm] Enable Liftoff by default on ia32 and x64"
> 
> This is a reland of 20f33823.
> The flakes that lead to the revert are hopefully fixed with
> https://crrev.com/c/1118171.
> 
> Original change's description:
> > [wasm] Enable Liftoff by default on ia32 and x64
> >
> > R=titzer@chromium.org, hablich@chromium.org
> >
> > Bug: v8:6600, chromium:787421
> > Change-Id: Ia8ae56ddef3b27b0721d5a66ff19abe098a2c6ca
> > Reviewed-on: https://chromium-review.googlesource.com/1109899
> > Reviewed-by: Ben Titzer <titzer@chromium.org>
> > Reviewed-by: Michael Hablich <hablich@chromium.org>
> > Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#53965}
> 
> TBR=titzer@chromium.org, hablich@chromium.org
> 
> Bug: v8:6600, chromium:787421
> Change-Id: Icfc6f5c7701f18891ede34edb2bc22a7c01c8d6d
> Reviewed-on: https://chromium-review.googlesource.com/1118485
> Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#54099}

TBR=titzer@chromium.org,hablich@chromium.org,clemensh@chromium.org

Change-Id: I0caa20c70ab18a8da4665b565d35801c3cf03fed
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6600, chromium:787421
Reviewed-on: https://chromium-review.googlesource.com/1119885Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54101}

src/flag-definitions.h

@@ -534,18 +534,9 @@ DEFINE_UINT(wasm_max_mem_pages, v8::internal::wasm::kV8MaxWasmMemoryPages,
             "maximum memory size of a wasm instance")
 DEFINE_UINT(wasm_max_table_size, v8::internal::wasm::kV8MaxWasmTableSize,
             "maximum table size of a wasm instance")
-// Enable liftoff by default on ia32 and x64. More architectures will follow
-// once they are implemented and sufficiently tested.
-#if V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X64
-DEFINE_BOOL(
-    wasm_tier_up, true,
-    "enable wasm baseline compilation and tier up to the optimizing compiler")
-#else
-DEFINE_BOOL(
-    wasm_tier_up, false,
-    "enable wasm baseline compilation and tier up to the optimizing compiler")
+DEFINE_BOOL(wasm_tier_up, false,
+            "enable basic tiering up to the optimizing compiler")
 DEFINE_IMPLICATION(future, wasm_tier_up)
-#endif
 DEFINE_IMPLICATION(wasm_tier_up, liftoff)
 DEFINE_DEBUG_BOOL(trace_wasm_decoder, false, "trace decoding of wasm code")
 DEFINE_DEBUG_BOOL(trace_wasm_decode_time, false,