Prepare the removal of x11-toolkits/qt5-declarative

devel/qt5-declarative has not been released since Qt 5.5.1, and it
starts to lead to runtime conflicts with qt5-quick if installed.

• No port is actually still using it (there are ports that had it as a dependency, but do not really require it -- bump these, and remove it).
• Remove it from the Qt 5 metaport.

Reported by: Armin Pirkovitsch
Reviewed by: rakuco
Approved by: rakuco (mentor)
Differential Revision: https://reviews.freebsd.org/D10673