Fix warnings building without libwacom
When the libwacom build option is set to false the compiler throws these warnings:
../udev/libinput-device-group.c:95:1: warning: ‘wacom_handle_ekr’ defined but not used [-Wunused-function]
95 | wacom_handle_ekr(struct udev_device *device,
| ^~~~~~~~~~~~~~~~
[205/237] Compiling C object 'libinput-test-suite@exe/test_test-tablet.c.o'.
../test/test-tablet.c:5440:1: warning: ‘verify_left_handed_touch_sequence’ defined but not used [-Wunused-function]
5440 | verify_left_handed_touch_sequence(struct litest_device *finger,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../test/test-tablet.c:5385:1: warning: ‘verify_left_handed_tablet_sequence’ defined but not used [-Wunused-function]
5385 | verify_left_handed_tablet_sequence(struct litest_device *tablet,
# | ^~~~~~~~~~~~~~~~
# | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Add the required guards to fix the warnings.
Fix #791 (closed).