MB: Remove a --target-devices-file flag for JUnit tests on android.

Not needed since it doesn't run in a device. It will enable us to run JUnit
tests on android on swarming too :) and more good stuff like flakiness dashboard

BUG=chromium:497757
R=kjellander@webrtc.org

Review-Url: https://codereview.webrtc.org/2531993003
Cr-Commit-Position: refs/heads/master@{#15268}
diff --git a/tools/mb/mb.py b/tools/mb/mb.py
index bf3e1f6..5ae0a7f 100755
--- a/tools/mb/mb.py
+++ b/tools/mb/mb.py
@@ -1091,11 +1091,11 @@
       test_cmdline = [
           self.PathJoin('bin', 'run_%s' % target),
           '--logcat-output-file', '${ISOLATED_OUTDIR}/logcats',
-          '--target-devices-file', '${SWARMING_BOT_FILE}',
-          '-v',
       ]
+      if test_type != 'junit_test':
+        test_cmdline += ['--target-devices-file', '${SWARMING_BOT_FILE}',]
       cmdline = (['./../../build/android/test_wrapper/logdog_wrapper.py']
-                 + logdog_command + test_cmdline)
+                 + logdog_command + test_cmdline + ['-v'])
     else:
       extra_files = ['../../testing/test_env.py']