Bug 1619961 - Change 'mach jstests' to not run tests with --jitflags=jstests. r=tcampbell

Running tests with different JIT flags by default is inconsistent with
jstests.py or mach jit-test.

Differential Revision: https://phabricator.services.mozilla.com/D65325

--HG--
extra : moz-landing-system : lando

testing/mach_commands.py

@@ -513,7 +513,6 @@ class SpiderMonkeyTests(MachCommandBase):
             python,
             os.path.join(self.topsrcdir, 'js', 'src', 'tests', 'jstests.py'),
             js,
-            '--jitflags=jstests',
         ] + params
 
         return subprocess.call(jstest_cmd)