[devil] Don't attempt to remove nothing when removing system apps.

devil/devil/android/tools/provision_devices.py

Index: devil/devil/android/tools/provision_devices.py
diff --git a/devil/devil/android/tools/provision_devices.py b/devil/devil/android/tools/provision_devices.py
index a021463cdb37235d9a6c4a0386c5220f4bc4543a..0f49878e3f722899761abad03b9be554f946059e 100755
--- a/devil/devil/android/tools/provision_devices.py
+++ b/devil/devil/android/tools/provision_devices.py
@@ -358,10 +358,11 @@ def _RemoveSystemApp(device, system_app):
     path = os.path.join(directory, system_app)
     if device.PathExists(path):
       found_paths.append(path)
-  if not found_paths:
+  if found_paths:
+    device.RemovePath(found_paths, force=True, recursive=True)
+  else:
     logger.warning('Could not find install location for system app %s',
                    system_app)
-  device.RemovePath(found_paths, force=True, recursive=True)
 
 def RemoveSystemApps(device, system_app_remove_list):
   """Attempts to remove the provided system apps from the given device.