[test] Remove flag that causes contradictions

Some test variants and fuzzers set their own GC interval, so the flag
specified in the regression test causes flag contradictions.
The test failure was flaky anyway, so this change is only a slight
reduction in reproducability, and the test will still be used as seed
for the fuzzers.

R=machenbach@chromium.org

Bug: chromium:1313475
Change-Id: I7c7084ab34fe46d691b841921d42a487cc8a1cad
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3576114Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79845}

test/mjsunit/regress/regress-1313475.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --expose-gc --invoke-weak-callbacks --random-gc-interval=2000
+// Flags: --expose-gc --invoke-weak-callbacks
 
 // We spawn a new worker which creates a Realm, then terminate the main thread
 // which will also terminate the worker.