package/hplip: remove includedir hack

The 0001-fix-make.patch which was added to the hplip package to remove
hardcoded paths to the libusb header introduced a solution that isn't
correct. When cross-compiling, $(includedir) is ${prefix}/include (i.e
/usr/include), so it is not the location where headers can be
found. Due to this, hplip.mk was overriding the includedir value with
--includedir which is not correct.

To replace this mechanism, this commit changes the patch to instead
use pkg-config (which is already used in other places in hplip
configure.in) to detect libusb. This way, we can get rid of the hack
and get a proper detection of libusb.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>