Input: gtco - remove driver

The driver has its own HID descriptor parsing code, that had and still
has several issues discovered by syzbot and other tools. Ideally we
should move the driver over to the HID subsystem, so that it uses proven
parsing code.  However the devices in question are EOL, and GTCO is not
willing to extend resources for that, so let's simply remove the driver.

Note that our HID support has greatly improved over the last 10 years,
we may also consider reverting 6f8d9e26

 ("hid-core.c: Adds all GTCO
CalComp Digitizers and InterWrite School Products to blacklist") and see
if GTCO devices actually work with normal HID drivers.

Link: https://lore.kernel.org/r/X8wbBtO5KidME17K@google.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>