Removed references to linux_gpu, which has been removed

BUG=426897
R=kbr@chromium.org,phajdan.jr@chromium.org,zmo@chromium.org

Review URL: https://codereview.chromium.org/800013002

Cr-Commit-Position: refs/heads/master@{#313978}

PRESUBMIT.py

@@ -1596,7 +1596,6 @@ def GetTryServerMasterForBot(bot):
   """
   # Potentially ambiguous bot names are listed explicitly.
   master_map = {
-      'linux_gpu': 'tryserver.chromium.gpu',
       'win_gpu': 'tryserver.chromium.gpu',
       'chromium_presubmit': 'tryserver.chromium.linux',
       'blink_presubmit': 'tryserver.chromium.linux',

PRESUBMIT_test.py

@@ -598,8 +598,6 @@ class TryServerMasterTest(unittest.TestCase):
   def testTryServerMasters(self):
     bots = {
         'tryserver.chromium.gpu': [
-            'linux_gpu',
-            'linux_gpu_triggered_tests',
             'win_gpu',
             'win_gpu_triggered_tests',
         ],

gpu/PRESUBMIT.py

@@ -11,7 +11,6 @@ for more details about the presubmit API built into depot_tools.
 def GetPreferredTryMasters(project, change):
   return {
     'tryserver.chromium.gpu': {
-      'linux_gpu': set(['defaulttests']),
       'win_gpu': set(['defaulttests']),
     }
   }