[transfer-engine] Remove Qt 4 daemon.

Depend on Qt 5 daemon for Qt 4 library. This fixes both packages trying to own
the same file (which mic will barf on, as well as being rather a bad idea).
[transfer-engine] Remove additional doc install rule from doc.pri.

qdoc seems to handle documentation installation itself. This install rule
installed a second copy of documentation to a different path.

How this worked previously, I am not entirely sure...