Eliminate location_href and location_base from the schema

[dralley]

location_href shouldn't have been in our schema originally. It was copied over from createrepo_c, but there it refers to a property of the individual repository layout rather than a unique identifier for the package. e.g. If a particular package is at a location RPMs/f/foo-1.2.3-4.noarch.rpm and you publish a repository containing that RPM, the actual location_href in the resulting metadata will be Packages/f/foo-1.2.3-4.noarch.rpm

Likewise with location_base.

We should remove the location_href and location_base fields entirely. This might be tricky from an API compatibility point of view, unfortunately.

[dralley]

(See the previous PR for some ideas whenever we get around to this. In the meantime I'm at least going to deprecate.)