Make net-im/telepathy-qt5 a slaveport of net-im/telepathy-qt4

net-im/telepathy-qt4 and net-im/telepathy-qt5 had very similar Makefiles and
use the same distfile. So it makes sense to combine them into slaveports.

Reviewed by: mat, rakuco
Approved by: rakuco (mentor)
Differential Revision: https://reviews.freebsd.org/D7898