Use “copy "i18n"” in km_KH locale

The custom stuff which was in LC_CTYPE of the km_KH locale seems
to be a very incomplete subset of what one gets by using
“copy "i18n"”. I cannot find anything special there which is not
in “copy "i18n"”, only lots of stuff which is missing.

	[BZ #20008]
	* locales/km_KH (LC_CTYPE): Use “copy "i18n"”.