Drop support for Qt5 in VLC 2.1.x branch.

Fixes bug 489508. qt5 use flag was buggy, and this configuration was not very well supported by upstream.
Since Qt5 is still masked in portage tree, there is a big chance that first VLC 2.2.x release will be before Qt5 is unmasked.

Package-Manager: portage-2.2.8-r2