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

sync/PRESUBMIT.py

Index: sync/PRESUBMIT.py
diff --git a/sync/PRESUBMIT.py b/sync/PRESUBMIT.py
index 87d68b4c7bc0506213881c5b526e6fdb10db5945..45f461e4060e10223e3f6d4f20578e78dfb3881a 100644
--- a/sync/PRESUBMIT.py
+++ b/sync/PRESUBMIT.py
@@ -11,10 +11,10 @@ for more details on the presubmit API built into gcl.
 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': set(['defaulttests']),