These were emptied out when SDL 1.2 was removed (358bd1235f07d8d577). I seem to recall
someone saying it might be worth keeping them around in case something needed to be put
back, but it's been a year and a half. Not much worth in keeping empty files.
This quells warnings from CMake about reserved target names, and reduces confusion about which `test` is intended: the wesnoth executable or the standard shell command.
