Revert "Add input device support"

Revert "Add input device support"

Apparently the:

[x] Squash commits

box was checked when merge request plymouth/plymouth!177 was merged.
Oops.

We want good commit messages for such a big change, though, so people
doing code spelunking later have a fighting chance of following what's
going on.

This reverts commit dacfb36b5714cd34791ab85d72629886075ff492.

Subsequents commits will bring it back, peicemeal.