keyboard: remove exceptions from storing pressed keys

keyboard: remove exceptions from storing pressed keys

These exceptions were added to prevent certain keys (modifiers and
synthetic layout switch key-events) from disabling keybindings (due to
the "nr_pressed_keys > 1" check). That check no longer exists, so the
exceptions should no longer be necessary.

Partially reverts e77330bc3fe7 and 3e2baa3f05ac.