x11-themes/adwaita-qt[45] move to a flavored version

• x11-themes/adwaita-qt4 -> adwaita-qt@qt4
• x11-themes/adwaita-qt5 -> adwaita-qt@qt5
• x11-themes/adwaita-common -> gone.

Approved by: portmgr (mat)
Differential Revision: https://reviews.freebsd.org/D15228