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

This reverts commit 85e6c4b6.

Reason for revert: All gc-stress bots are unhappy: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux%20-%20gc%20stress/34544/overview

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: I91fde3a35eece61e1dfa8b81f57fcda465ce5882
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3046178
Auto-Submit: Clemens Backes <clemensb@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@{#75869}

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