Removed references to mac_gpu, which has been removed

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index c875e48f00d9bec495598fa169ed8ca0bfa31c56..64c34be90f99fdb832190adfb17cfc66a5adf592 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -1603,7 +1603,6 @@ def GetTryServerMasterForBot(bot):
   # Potentially ambiguous bot names are listed explicitly.
   master_map = {
       'linux_gpu': 'tryserver.chromium.gpu',
-      'mac_gpu': 'tryserver.chromium.gpu',
       'win_gpu': 'tryserver.chromium.gpu',
       'chromium_presubmit': 'tryserver.chromium.linux',
       'blink_presubmit': 'tryserver.chromium.linux',
@@ -1705,7 +1704,6 @@ def GetDefaultTryConfigs(bots=None):
       'mac_chromium_compile_dbg_ng': ['defaulttests'],
       'mac_chromium_rel': ['defaulttests'],
       'mac_chromium_rel_ng': ['defaulttests'],

[Ken Russell (switch to Gerrit), 2014/12/12 18:47:47]

Same question as for the CL removing linux_gpu and win_gpu: will
mac_chromium_rel_ng unconditionally run the GPU tests, or are the tests that are
run filtered by the "standard_tests" list above?

[Sergiy Byelozyorov, 2014/12/15 16:00:23]

I think 'defaulttests' is just a placeholder, which is not used anywhere. Pawel,
WDYT?

[Paweł Hajdan Jr., 2014/12/15 16:01:36]

Yeah, this is just a dummy value at this point. testfilter has no effect on
recipe-based bots.

-      'mac_gpu': ['defaulttests'],
       'mac_nacl_sdk_build': ['compile'],
       'win_chromium_compile_dbg': ['defaulttests'],
       'win_chromium_dbg': ['defaulttests'],
@@ -1799,7 +1797,6 @@ def GetPreferredTryMasters(project, change):
       'linux_gpu',
       'mac_chromium_compile_dbg_ng',
       'mac_chromium_rel_ng',
-      'mac_gpu',
       'win_chromium_compile_dbg',
       'win_chromium_rel',
       'win_chromium_x64_rel',