Remove old panel focus workaround

Simplify panel focus from shortcut. The logic was done to fix bug 472909 (focus not getting back to proper window after opening kickoff with shortcut), replace it with a better fix in plasma-workspace.

See plasma-workspace!3868 (merged)

That logic caused a breakage in the shortcut to give panel focus, as it became necessary to press it twice to give panel focus for the first time after plasma startup