[kio-extras] Use new activities icon
Summary:
Use the new icon added in D22155.
Test Plan: Open the Dolphin view context menu and visit "activities:".
Reviewers: Plasma, VDG, ndavis
Reviewed By: VDG, ndavis
Subscribers: kde-frameworks-devel, VDG, kfm-devel, Plasma
Tags: Dolphin, Frameworks
Differential Revision: https://phabricator.kde.org/D22172