Really build without tdb

The debian/control file was re-generated by dh_gnome_clean from debian/control.in which was not patched to drop the libtdb dependency. In addition, debian/rules was not ensuring that the tdb support was disable, but merely reverted to autodetection.

This caused libtdb-dev to be available at build time and enabled after autodetection.

To ensure this does not happen, patch the template file as well, put libtdb-dev in Build-Conflicts to ensure it's not installed in the build chroot and force-disable it from debian/rules.

This also means that some cache-related symbols are no longer exported.