Enable chrome_public_test_apk on android-pie-arm64-rel

With crbug.com/1166997 fixed, the test suite turns green in trybot now.
The test pool usage is a bit high (http://shortn/_unkbNiWpws), but the
swarming task pending time is acceptable (http://shortn/_WCL47QSQOd),
despite the one on 1/19 due to test regression.

Bug: 1111436
Change-Id: Ied1639acdd124d041e2d55dbe02b66a5aa661214
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2639370Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Haiyang Pan <hypan@google.com>
Cr-Commit-Position: refs/heads/master@{#845418}

testing/buildbot/chromium.android.json

@@ -41725,7 +41725,6 @@
           "--git-revision=${got_revision}",
           "--test-launcher-filter-file=../../testing/buildbot/filters/android.pie_arm64_rel.chrome_public_test_apk.filter"
         ],
-        "experiment_percentage": 100,
         "merge": {
           "args": [
             "--bucket",

testing/buildbot/test_suite_exceptions.pyl

@@ -790,8 +790,6 @@
         'args': [
           '--test-launcher-filter-file=../../testing/buildbot/filters/android.pie_arm64_rel.chrome_public_test_apk.filter', # https://crbug.com/1010211
         ],
-        # TODO(crbug.com/1111436): Remove experimental when it works fine.
-        'experiment_percentage': 100,
       },
       'android-pie-x86-rel': {
         'args': [