Fix syntax error in Japanese translation
Remove remenants of mob code

Since minetest has no mobs within the core anymore, I suppose these
settings and code should go. Any mod that uses `minetest.setting_getbool`
will work with no problem since the default return value is `false`.
Merge remote-tracking branch 'minetest/master'

Conflicts:
	po/ja/minetest.po
	src/environment.cpp