_main.cfg: change textdomain name

As it was, it was overwriting the default wesnoth textdomain.  Thanks
trewe.
Revert "_main.cfg: change textdomain name"

This reverts commit 5b1129abe4567bac63fb950242b6b5d80536a1f3.
_main.cfg: change textdomain name

As it was, it was overwriting the default wesnoth textdomain.  Thanks
trewe.
Only commit changes to _main.cfg this time, not to other files.