move kcrash link to dolphin app (which is the effective user)

Summary:
to successfully use kcrash when linking with as-needed (which is a default
flag on many linux distros) one also needs to call KCrash::initialize.
this call happens in the app's main.cpp. as such the kcrash link target
on the dolphinprivate library doesn't do anything for dolphinprivate but
only kicks into action for dolphin itself.
to avoid confusion and make it clear that kcrash is only initialized in the
application scope the KF5::Crash link target is now on the application
target, not the library target.

(this makes no difference in the output, kcrash was still correctly linked
 via dolphinprivate; but only for kdeinit_dolphin, dolphinprivate did
 not get linked to it with as-needed)

Test Plan: builds; links as expected

Reviewers: elvisangelaccio, #dolphin

Reviewed By: elvisangelaccio, #dolphin

Subscribers: kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D16896