ozone: remove experiment_percentage from ozone_unittests

The ozone_unittests have been running successfully on
the linux-ozone-rel bot with experiment_percentage: 100 for
more than one month.

Now, we can remove the experiment_percentage from it.

Bug: 700309
Change-Id: I0a82d354769d75cce65063a95e18c40b2bcae79e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1571409Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#654809}

testing/buildbot/chromium.linux.json

@@ -5121,7 +5121,6 @@
     ],
     "gtest_tests": [
       {
-        "experiment_percentage": 100,
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [

testing/buildbot/test_suites.pyl

@@ -4115,9 +4115,7 @@
 
     'ozone_linux_gtests': {
       'services_unittests': {},
-      'ozone_unittests': {
-        'experiment_percentage': 100,
-      },
+      'ozone_unittests': {},
     },
 
     'performance_smoke_test_isolated_scripts': {