Enable chrome_public_smoke_tests on android-marshmallow-x86-rel CQ

It runs fine in the past week: http://shortn/_IILmyFI7dT
Also the host pool (http://shortn/_jSF6ym5jrX) and test
pool (http://shortn/_nTRsiMFi2n) are in good shape.

Bug: 1127110
Change-Id: I334ec90bd9eb5cd736894d5762f764a2326c874d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2575596
Auto-Submit: Haiyang Pan <hypan@google.com>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833910}

testing/buildbot/chromium.android.json

@@ -31996,7 +31996,6 @@
           "--recover-devices",
           "--avd-config=../../tools/android/avd/proto/generic_android23.textpb"
         ],
-        "experiment_percentage": 100,
         "merge": {
           "args": [
             "--bucket",

testing/buildbot/test_suite_exceptions.pyl

@@ -728,11 +728,6 @@
     'remove_from': [
       'android-code-coverage-native', # https://crbug.com/1018780
     ],
-    'modifications': {
-      'android-marshmallow-x86-rel': {
-        'experiment_percentage': 100, # crbug.com/1127110
-      },
-    },
   },
   'chrome_public_test_apk': {
     'remove_from': [