Remove <linux/input.h> include from test/x11comp.c

libxkbcommon 0.4.3 introduces a new test, x11comp, which does not build
on non-Linux OSes because of the unconditional <linux/input.h> include.

This seems not needed even on Linux, so attached there is a simple patch
to remove it.

https://bugs.freedesktop.org/show_bug.cgi?id=83551

Signed-off-by: Ran Benita <ran234@gmail.com>
test: make most tests portable by copying linux/input.h locally

There is really no reason to deny these tests from different platforms
only for a few #defines.

The only linux-only test (or test program, it is not run by make check)
is interactive-evdev, which actually uses evdev.

Signed-off-by: Ran Benita <ran234@gmail.com>