Win: do not suggest user to install Qt development libraries

We do not ship Qt GUI anymore in master-1.12 branch

Change-Id: Ie56f7a0e76e9179d43dd616a49418daeef745a19
Reviewed-on: https://code.wireshark.org/review/5688
Reviewed-by: Graham Bloice <graham.bloice@trihedral.com>