Set empty list as default value for extra_args in run_on_app

Seems to be what the code below is doing anyway.

Change-Id: I9cf578d1e6ca9d7c5ae2de11f04b20b9e661dc28

tools/run_on_app.py

diff --git a/tools/run_on_app.py b/tools/run_on_app.py
index d93e3c0..3a0ea7c 100755
--- a/tools/run_on_app.py
+++ b/tools/run_on_app.py
@@ -386,9 +386,7 @@
     return 'deploy' if options.compiler == 'r8' else 'proguarded'
   return options.type
 
-def run_with_options(options, args, extra_args=None, stdout=None, quiet=False):
-  if extra_args is None:
-    extra_args = []
+def run_with_options(options, args, extra_args=[], stdout=None, quiet=False):
   app_provided_pg_conf = False;
   # todo(121018500): remove when memory is under control
   if not any('-Xmx' in arg for arg in extra_args):