HID: asus: Simplify skipping of mappings for Asus T100CHI keyboard-dock

Before this commit the code was trying to keep the mapping for the
left mouse-button, do avoid the hidinput_has_been_populated() check
in hid-input.c from triggering and causing the touchpad input_dev ro
get cleaned up.

But the hidinput_has_been_populated() check happens after the
input_configured callback which sets up all the input bit for the
touchpad, so there is no need to preserve the left button mapping.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>