[kitemviews] Change the search in Desktop Behavior/Activities to more in line with other search labels
Summary: This patch removes the "Search:" portion of Activities (in System Settings, Desktop Behavior --> Workspace) and adds "Search..." to the search field.
Reviewed By: VDG, ngraham
Subscribers: ngraham, kde-frameworks-devel
Maniphest Tasks: T10258
Differential Revision: https://phabricator.kde.org/D18046