kded: Remove leftover KScreenDpms dependency
This was added as part of !147 (merged), but the part of the code that needed the dependency was removed in !237 (merged).
The QScreen include was also only used by the same removed code.
This was added as part of !147 (merged), but the part of the code that needed the dependency was removed in !237 (merged).
The QScreen include was also only used by the same removed code.