Removed everything which got split out

In the New Architecture for printing we switch to an all-IPP workflow
with PPD files being abolished and classic CUPS printer drivers
replaced by Printer Applications (software emulation of driverless IPP
printers).

To conserve the functionality of the CUPS filters which got developed
over the last 20+ years into a PPD-less, IPP-driven world without
having to maintain and include the legacy PPD support in OS
distributions and other system environments, the original cups-filters
package got split into 5 separate packages: libcupsfilters, libppd,
cups-filters, braille-printer-app, and cups-browsed, with
libcupsfilters and braille-printer-app not containing PPD file support
code any more and cups-browsed being planned to drop explicit use of
PPD files.

This commit drops everything from the cups-filters repository which
got split out into the other 4, new repositories.

What remains are the CUPS filter executables, from which most are
wrappers around filter functions implemented in the libcupsfilters and
libppd libraries, backends, the "driverless" utility for setting up
driverless printers with classic printer setup tools, and auxiliary
files (PPD files, *.drv files, MIME rules, ...).

This package is needed for using CUPS 2.x with filters from
libcupsfilters (2.x) and libppd.

It is not needed/does not make sense to be used with CUPS 3.x or the
CUPS Snap (or any other containerized CUPS implementation). If you
need printer drivers for such CUPS versions, use Printer Applications.