Revert "Reland "[sparkplug] Enable sparkplug by default on desktop""

This reverts commit 0f79565b.

Reason for revert: Still breaking gc-stress...
https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux%20-%20gc%20stress/34581/overview

Original change's description:
> Reland "[sparkplug] Enable sparkplug by default on desktop"
>
> This is a reland of 85e6c4b6
> GC-stress issue was flushing, fixed with https://crrev.com/c/3048172.
> Relanding without changes.
>
> TBR=verwaest@chromium.org
>
> Original change's description:
> > [sparkplug] Enable sparkplug by default on desktop
> >
> > Bug: v8:11420
> > Change-Id: I07ac7f30b5ffffe40170ac15d5df0d3bf8a53523
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3041418
> > Auto-Submit: Leszek Swirski <leszeks@chromium.org>
> > Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> > Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#75868}
>
> Bug: v8:11420
> Change-Id: I44ac0e4a5df07db79fa50db3134cdae3af41c88c
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3053588
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#75916}

Bug: v8:11420
Change-Id: I5f96a76392c4ea0d1c9192e697d954de086aa4f4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3054113
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#75921}

src/flags/flag-definitions.h

@@ -190,13 +190,6 @@ struct MaybeBoolFlag {
 #define ENABLE_SPARKPLUG false
 #endif
 
-#if ENABLE_SPARKPLUG && !defined(ANDROID)
-// Enable Sparkplug by default on desktop-only.
-#define ENABLE_SPARKPLUG_BY_DEFAULT true
-#else
-#define ENABLE_SPARKPLUG_BY_DEFAULT false
-#endif
-
 // Supported ARM configurations are:
 //  "armv6":       ARMv6 + VFPv2
 //  "armv7":       ARMv7 + VFPv3-D32 + NEON
@@ -654,8 +647,7 @@ DEFINE_INT(interrupt_budget_scale_factor_for_top_tier, 20,
 #else
 #define FLAG FLAG_READONLY
 #endif
-DEFINE_BOOL(sparkplug, ENABLE_SPARKPLUG_BY_DEFAULT,
-            "enable Sparkplug baseline compiler")
+DEFINE_BOOL(sparkplug, false, "enable experimental Sparkplug baseline compiler")
 DEFINE_BOOL(always_sparkplug, false, "directly tier up to Sparkplug code")
 DEFINE_BOOL(sparkplug_on_heap, false, "compile Sparkplug code directly on heap")
 #if ENABLE_SPARKPLUG