HID: elo: clear BTN_LEFT mapping

[ Upstream commit 9abd04af951e5734c9d5cfee9b49790844b734cf ]

ELO devices have one Button usage in GenDesk field, which makes hid-input map
it to BTN_LEFT; that confuses userspace, which then considers the device to be
a mouse/touchpad instead of touchscreen.

Fix that by unmapping BTN_LEFT and keeping only BTN_TOUCH in place.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>