Fix locale package generation.

The package class has code to generate split language pack packages,
one, and each of those provides ${PN}-locale, so installing ${PN}-locale
ends up installing a language at random. Make ${PN}-locale a meta package
instead, and have it RDEPEND on the actual locale packages.
This allows a distro to install all translations without caring of which
are actually shipped by a particular package.
The dependency for individual locale packages on virtual-locale-* is
removed, to allow installing eglibc-locale-locale.alias (otherwise depending
on a non-existing virtual-locale-locale.alias).
Install all locales provided by eglibc.

By installing eglibc-locale, we ensure that all locale files (sources,
translations and binary locales) are installed in the final image.