Add way for the user to forget previously used printers.

We keep track of historical printers but some of them may disappear
forever, say the user changes his printer. In such a case the print
system has no idea that the previous printer will never appear so
this change allows the user to remove historical printers.

In the all printers list the user can now long press on a printer
and if the printer is available he can select it from the context
menu. If the printer was used before regardless if it is active the
user may choose to forget it.

bug:11282742

Change-Id: Idc2dda70920ad045149eea1bcfc75ad1992827e9