Convert manually triggered try runs to use bots without _swarming prefix.

base/PRESUBMIT.py

Index: base/PRESUBMIT.py
diff --git a/base/PRESUBMIT.py b/base/PRESUBMIT.py
index 758a79053ae57eaeff62d1f39a468991817829d0..a5913f1666731ab91f43cc44bd5ae8a78095f9d5 100644
--- a/base/PRESUBMIT.py
+++ b/base/PRESUBMIT.py
@@ -92,12 +92,12 @@ def CheckChangeOnCommit(input_api, output_api):
 def GetPreferredTryMasters(project, change):
   return {
     'tryserver.chromium.linux': {
-      'linux_chromium_rel_swarming': set(['defaulttests']),
+      'linux_chromium_rel': set(['defaulttests']),
     },
     'tryserver.chromium.mac': {
-      'mac_chromium_rel_swarming': set(['defaulttests']),
+      'mac_chromium_rel': set(['defaulttests']),
     },
     'tryserver.chromium.win': {
-      'win_chromium_rel_swarming': set(['defaulttests']),
+      'win_chromium_rel': set(['defaulttests']),
     }
   }