Make the layout tests non-experimental on K Phone Tester (dbg)

Bug: 790265,824539
Change-Id: Ic34ea3ae7f2aa3221edb436ed443a7c943cc1d43
Reviewed-on: https://chromium-review.googlesource.com/c/1260202Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596427}

testing/buildbot/chromium.android.json

@@ -3208,7 +3208,6 @@
           "--android",
           "--additional-driver-flag=--use-gpu-in-tests"
         ],
-        "experiment_percentage": 100,
         "isolate_name": "webkit_layout_tests_exparchive",
         "merge": {
           "args": [

testing/buildbot/test_suite_exceptions.pyl

@@ -1370,7 +1370,6 @@
           # software fallback, SwiftShader, isn't yet for 32-bit ARM.
           '--additional-driver-flag=--use-gpu-in-tests',
         ],
-        'experiment_percentage': 100, # crbug.com/824539
       },
       # chromium.fyi
       'linux-blink-animation-use-time-delta': {