touchpad: revert the clickpad detection mechanism

touchpad: revert the clickpad detection mechanism

Use the previous heuristics to detect clickpads where a touchpad was
handled as a clickpad when:

 - The property INPUT_PROP_BUTTONPAD is set
 - The property INPUT_PROP_BUTTONPAD is NOT set but the touchpad only
   has BTN_LEFT

Revert a37d6dcc9c2ec7ebd0d3609e01da1cfcec28db6e:
"touchpad: if we have a right button, let's assume it's not a clickpad"
MR:  https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/614
BUG: https://gitlab.freedesktop.org/libinput/libinput/-/issues/595

Fix #704

Signed-off-by: José Expósito <jose.exposito89@gmail.com>