hwdb: weed out key defines which do not designate events

The defines

KEY_MAX
KEY_CNT
KEY_MIN_INTERESTING
BTN_MISC
BTN_MOUSE
BTN_JOYSTICK
BTN_GAMEPAD
BTN_DIGI
BTN_WHEEL
BTN_TRIGGER_HAPPY

mark start/end of key blocks and do not designate events.

Exclude them from the list of recognized key events.