Remove unnecessary testing in browser.test_pthread_gcc_atomic_fetch_and_op (#12333)

We tested heavily because of the old regex stuff in fastcomp pthreads.

Still seems useful to ensure one pthreads tests has all opt levels, but
remove excessive debug levels.

This makes the test 2x faster.

Author: kripken

tests/test_browser.py

@@ -3613,10 +3613,8 @@ def test_pthread_main_thread_blocking(self, name):
   @no_firefox('https://bugzilla.mozilla.org/show_bug.cgi?id=1666568')
   @requires_threads
   def test_pthread_gcc_atomic_fetch_and_op(self):
-    # We need to resort to using regexes to optimize out SharedArrayBuffer when pthreads are not supported, which is brittle!
-    # Therefore perform very extensive testing of different codegen modes to catch any problems.
     for opt in [[], ['-O1'], ['-O2'], ['-O3'], ['-Os']]:
-      for debug in [[], ['-g1'], ['-g2'], ['-g4']]:
+      for debug in [[], ['-g']]:
         args = opt + debug
         print(args)
         self.btest(path_from_root('tests', 'pthread', 'test_pthread_gcc_atomic_fetch_and_op.cpp'), expected='0', args=args + ['-s', 'INITIAL_MEMORY=64MB', '-s', 'USE_PTHREADS=1', '-s', 'PTHREAD_POOL_SIZE=8'])