Revert "Move linux-chromeos-chrome's browser_tests into its own swarming pool."

This reverts commit 7032611d.

Reason for revert: No more BOT_DIEDs?

Original change's description:
> Move linux-chromeos-chrome's browser_tests into its own swarming pool.
>
> To prevent it from leaving junk around on the machine that causes
> other tests in that same pool to fail.
>
> Bug: 1039746
> Change-Id: I58a9bc242c56f5d7af196335cdd7d621cdb90a15
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1995779
> Reviewed-by: John Budorick <jbudorick@chromium.org>
> Commit-Queue: Ben Pastene <bpastene@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#730595}

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1039746
Change-Id: I488153b4319b162b7f8b4c809469104a0360ee30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2133233Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756003}

testing/buildbot/chrome.ci.json

@@ -2105,7 +2105,7 @@
           "dimension_sets": [
             {
               "os": "Ubuntu-16.04",
-              "pool": "chrome.tests.browser_tests_killer",
+              "pool": "chrome.tests.template",
               "ssd": "0"
             }
           ],

testing/buildbot/chrome.json

@@ -1364,7 +1364,7 @@
           "dimension_sets": [
             {
               "os": "Ubuntu-16.04",
-              "pool": "chrome.tests.browser_tests_killer",
+              "pool": "chrome.tests.template",
               "ssd": "0"
             }
           ],

testing/buildbot/test_suite_exceptions.pyl

@@ -520,14 +520,6 @@
         'args': [
           '--test-launcher-filter-file=../../testing/buildbot/filters/chromeos.browser_tests.filter',
         ],
-        # TODO(https://crbug.com/1039746): Move this back to the main pool.
-        'swarming': {
-          'dimension_sets': [
-            {
-              'pool': 'chrome.tests.browser_tests_killer',
-            },
-          ],
-        },
       },
       'linux-chromeos-code-coverage': {
         'swarming': {