Issue #4116: Make infile and outfile parameters of flrender script from python-abp optional

tests/test_render_script.py

 # This file is part of Adblock Plus <https://adblockplus.org/>,
 # Copyright (C) 2006-present eyeo GmbH
 #
 # Adblock Plus is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 3 as
 # published by the Free Software Foundation.
 #
 # Adblock Plus is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
@@ skipping 93 matching lines @@
     stdout, stderr = proc.communicate(input=test_in)
     return proc.returncode, stderr.decode('utf-8'), stdout.decode('utf-8')
 
 
 @pytest.mark.parametrize('test_input, args', [
     ('None', ["'simple.txt'", 'str(dstfile)']),
     ('None', ["'simple.txt'"]),
     ("rootdir.join('simple.txt').read()", []),
 ])
 def test_render_no_includes(test_input, args, rootdir, dstfile):
-    _locals = locals()
     test_input = eval(test_input)
     args = list(map(eval, args))
     _, _, stdout = run_script(*args, cwd=str(rootdir), test_in=test_input)
 
     if len(args) > 1:
         output = dstfile.read()
     else:
         output = stdout
 
     assert 'Ok' in output
@@ skipping 79 matching lines @@
 
 @pytest.mark.slowtest
 def test_failed_web_include(rootdir, dstfile, webserver_port):
     url = 'http://localhost:{}/missing.txt'.format(webserver_port)
     webinc = rootdir.join('webinc.txt')
     webinc.write('[Adblock]\n%include {}%'.format(url))
     code, err, _ = run_script(str(webinc), str(dstfile))
     assert code == 1
     assert err.startswith(
         "HTTP 404 Not found: '{0}' when including '{0}'".format(url))