evdev: Cleanup mouse and keyboard plugins

evdev: Cleanup mouse and keyboard plugins

Remove fallback event0 device usage. All available devices should be
detected automatically from DeviceDiscovery either through udev or the
static fallback discovery method. This also removes the never used 'key'
argument, which was pulled over from Qt4.

Change-Id: Iffe8bd80f0770664024019a220cbbc6f98843340
Reviewed-by: Girish Ramakrishnan <girish.1.ramakrishnan@nokia.com>