6934d54417 added an optional dependency
on karchive. This also means that it doesn't merely depend on Qt and a
small number of third-party libs anymore and needs to moved to tier 2.
REVIEW: 127015
They were already disabled when building with Qt >= 5.3 in commit
3d45b270ea because Qt has better plugins
for those image formats. Now that we depend on Qt 5.3 we can remove
them.
REVIEW: 124636
Heiko Becker