debug_CA mode: don't need to play through turn any more ...

... for initializing the ai and self.data tables.  This can now be done
with a bogus call to [modify_ai].
debug_CA mode: fix missing library issue
debug_CA mode: change message
debug_CA mode: remove "Kill Unit under Cursor" menu option

This is now available in mainline anyway.
Local debug_utils: remove Wesnoth Lua Pack dependency
debug_CA mode: do not show data table content in message

... only in chat window.