WebRTC: Remove Valgrind based FYI bots.

masters/master.client.webrtc.fyi/slaves.cfg

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 slaves = [
   # Linux
   {
     'master': 'WebRTCFYI',
     'os': 'linux',
     'version': 'precise',
     'bits': '64',
     'builder': [
       'Linux LSan (and ASan)',
-      'Linux TsanRV',
     ],
-    'hostname': 'vm%d-m3' % i,
-  } for i in [4, 31]
-] + [
-  # Mac
-  {
-    'master': 'WebRTCFYI',
-    'os': 'mac',
-    'version': '10.6',  # Notice 10.6 due to lack of Valgrind support on newer.
-    'bits': '64',
-    'builder': [
-      'Mac 10.6 Memcheck',
-      'Mac 10.6 TSan',
-    ],
-    'hostname': 'vm%d-m3' % i,
-  } for i in [653, 665]
-] + [
+    'hostname': 'vm31-m3',
+  },
   # Windows
   {
     'master': 'WebRTCFYI',
     'os': 'win',
     'version': 'win7',
     'bits': '64',
     'builder': [
       'Win Tsan',
     ],
-    'hostname': 'vm%d-m3' % i,
-  } for i in [193]
+    'hostname': 'vm193-m3',
+  }
 ]