Revert "[test] Initialize slow-dcheck runtime flag with compile time value"

This reverts commit 2c1e4aa9.

Reason for revert:
https://ci.chromium.org/buildbot/client.v8.ports/V8%20Linux%20-%20arm64%20-%20sim%20-%20debug/11591

Original change's description:
> [test] Initialize slow-dcheck runtime flag with compile time value
> 
> This makes sure slow dchecks are part of the snapshot when the compile
> time flag is set. It'll also obviate the need to set the runtime flag
> in general, making configurations simpler.
> 
> It's still possible to opt out at runtime for the non-snapshot dchecks
> using the negated runtime flag.
> 
> Bug: v8:7853
> Change-Id: Iadfc46ed691d32e9d39717e2ea0383e784660d1d
> Reviewed-on: https://chromium-review.googlesource.com/1105050
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#53819}

TBR=machenbach@chromium.org,cbruni@chromium.org,jgruber@chromium.org,szuend@google.com

Change-Id: If209aa824749f358a892218dda99c30b1a63b99d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7853
Reviewed-on: https://chromium-review.googlesource.com/1105857Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53830}

src/flag-definitions.h

@@ -1136,7 +1136,7 @@ DEFINE_NEG_IMPLICATION(gdbjit, compact_code_space)
 
 // checks.cc
 #ifdef ENABLE_SLOW_DCHECKS
-DEFINE_BOOL(enable_slow_asserts, true,
+DEFINE_BOOL(enable_slow_asserts, false,
             "enable asserts that are slow to execute")
 #endif