ozone-linux: remove experiment_percentage from content_unittests

The content_unittests have been running by the linux-ozone-rel
bot for a couple of weeks since 06 of August without any failures.

Thus, remove the experiment percentage.

R=sky@chromium.org

Bug: 700309
Change-Id: Ib9c7e4f29c8bebc808b23bfb8c10358816e7d793
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1764139Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#689512}

testing/buildbot/chromium.linux.json

@@ -7685,7 +7685,6 @@
         "args": [
           "--ozone-platform=headless"
         ],
-        "experiment_percentage": 100,
         "merge": {
           "args": [],
           "script": "//testing/merge_scripts/standard_gtest_merge.py"

testing/buildbot/test_suites.pyl

@@ -4405,7 +4405,6 @@
       'services_unittests': {},
       'ozone_unittests': {},
       'content_unittests': {
-        'experiment_percentage': 100,
         'args': [
           '--ozone-platform=headless',
         ],