webkitpy: clean up a bunch of test scaffolding

webkitpy: clean up a bunch of test scaffolding
https://bugs.webkit.org/show_bug.cgi?id=76973

Reviewed by Eric Seidel.

There were several helper modules in the webkitpy.test package
that appear to only be used by executive_unittest.py. I am
rolling them all into that file to make that clearer.

* Scripts/webkitpy/common/system/executive_unittest.py:
(ExecutiveTest.test_run_command_args_type):
(ExecutiveTest.test_run_command_with_unicode):
(ExecutiveTest.test_running_pids):
(command_line):
(main):
* Scripts/webkitpy/common/system/fileutils.py: Removed.
* Scripts/webkitpy/test/cat.py: Removed.
* Scripts/webkitpy/test/cat_unittest.py: Removed.
* Scripts/webkitpy/test/echo.py: Removed.
* Scripts/webkitpy/test/echo_unittest.py: Removed.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105935 268f45cc-cd09-0410-ab3c-d52691b4dbfc