xbps-src: hooks: reorganize some hooks.

The strip-and-debug-pkgs/generate-runtime-deps hooks have been moved
to the pre-pkg stage, and are run before prepare-32bit; this way dependencies
are collected correctly in all cases.
xbps-src: remove WIP repo delta support.

- it never worked correctly
- it's WIP and looks like it will be stalled forever
- won't be necessary anymore with xbps-0.42