foomatic-filters: fix CUPS directory config

foomatic-filters: fix CUPS directory config

- use CUPS_SERVERBIN to configure the CUPS directory
- the removed variables are not used anymore

Fix the following warning:
WARNING: QA Issue: foomatic-filters: Files/directories were installed but not shipped
  /usr/lib64
  /usr/lib64/cups
  /usr/lib64/cups/filter
  /usr/lib64/cups/backend
  /usr/lib64/cups/filter/foomatic-rip
  /usr/lib64/cups/backend/beh

(From OE-Core rev: 141621d956ea66a026b3571c3e0d30f1ab43961e)

Signed-off-by: Constantin Musca <constantinx.musca@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>