Make zypp plugin configurable, 2 deprecated macros

Hi Arvin,

- remove 2 deprecated macros:
I noticed deprecated macros in configure.ac. It's just a suggestion (tested on debian, suse 12, fedora)

- make zypp plugin configurable:
recent commits made zypp plugin mandatory (few files are installed disregard the --disable-zypp configuration option).

Regards
O.