Revert "Load the keyboard on-demand"

This reverts commit 5c39795b.

This unfortuntaely introduces the regression on the phone where there's
multiple bugs preset,

- Keyboard can no longer be closed using close button, or removing
  focus.
- Opening keyboard makes application get no input events, making it look
  like it is crashed/stuck or hung.

I failed to reproduce this bug on desktop unfortunately.

CCMAIL: Aleix Pol <aleixpol@kde.org>