Kill PDE build support for RPMs.

PDE building RPM-packaged plug-ins has long proved to be fragile
to maintain, so a concerted effort has been made to move all RPM
packaged plug-ins in Fedora to Tycho. All future RPM packages must
use Tycho to build in Fedora.

Change-Id: I2f47daff75d8c51d92b2991c93b733eab9b8af8b
Signed-off-by: Mat Booth <mat.booth@redhat.com>
Reviewed-on: https://git.eclipse.org/r/71435