Remove opkg_internal_use_only and fix associated assumptions RE pkg->provides.

It appears that the opkg_internal_use_only provides string was introduced to
bandaid over problems with assuming that the pkg->provides, pkg->provides_str
and pkg->provides_count are all the same length. As each pkg provides itself,
the pkg->provides array was one longer than the str and count fields. Most of
the uses of pkg->provides did not take this into account.

This behaviour has been changed. pkg->provides is now pkg->provides_count long
and it is pkg->provides_str which is shorter by one.

Associated dead code has also been removed.

git-svn-id: http://opkg.googlecode.com/svn/trunk@277 e8e0d7a0-c8d9-11dd-a880-a1081c7ac358