[benchmarking] Turn off angle_perftests from nexus5x bot.

Apparently since nexus5x is running Android M, these results are
not useful to Angle developers.

R=jmadill@chromium.org, ynovikov@chromium.org

Bug: 1030840
Change-Id: I1883bba49c8b471cc73746dcc15dfaf8764c6e40
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1986971Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728604}

testing/buildbot/chromium.perf.json

@@ -833,46 +833,6 @@
   },
   "android-nexus5x-perf": {
     "isolated_scripts": [
-      {
-        "args": [
-          "--gtest-benchmark-name",
-          "angle_perftests",
-          "--shard-timeout=300"
-        ],
-        "isolate_name": "angle_perftests",
-        "merge": {
-          "script": "//tools/perf/process_perf_results.py"
-        },
-        "name": "angle_perftests",
-        "override_compile_targets": [
-          "angle_perftests"
-        ],
-        "swarming": {
-          "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "device_os": "MMB29Q",
-              "device_os_flavor": "google",
-              "device_type": "bullhead",
-              "os": "Android",
-              "pool": "chrome.tests.perf"
-            }
-          ],
-          "expiration": 7200,
-          "hard_timeout": 19800,
-          "ignore_task_failure": false,
-          "io_timeout": 19800,
-          "shards": 1
-        },
-        "trigger_script": {
-          "args": [
-            "--multiple-dimension-script-verbose",
-            "True"
-          ],
-          "requires_simultaneous_shard_dispatch": true,
-          "script": "//testing/trigger_scripts/perf_device_trigger.py"
-        }
-      },
       {
         "args": [
           "--gtest-benchmark-name",

tools/perf/core/perf_data_generator.py

@@ -391,14 +391,6 @@ BUILDERS = {
         'num_shards': 1,
         'type': TEST_TYPES.GTEST,
       },
-      {
-        'isolate': 'angle_perftests',
-        'num_shards': 1,
-        'type': TEST_TYPES.GTEST,
-        'extra_args': [
-            '--shard-timeout=300'
-        ],
-      },
       {
         'isolate': 'base_perftests',
         'num_shards': 1,