Seems that in current version of the ebuild the daap useflag has no effect. Maybe I miss something.
I agree, it looks like leftover cruft. I have pushed the changes to the overlay[1], to give people the chance to disagree before it hits the tree. [1]: http://git.overlays.gentoo.org/gitweb/?p=proj/kde.git;a=commitdiff;h=406f4676a61e3d7bec807eba0862583052023cbe
Removed in 2.8.0