inputpanel: ignore requested output
While there's specific hardware where the IM could benefit from requesting to be shown on a specific output, it effectively never has enough information to choose a useful output - and the protocol doesn't allow setting a null output to indicate that the compositor should do the choice. To avoid showing the OSK on the wrong output, always put it on the active output and ignore what the IM client requests.
(cherry picked from commit 7cb4b51d)