xcb-proto had a dependency on python-native as it builds and installs a Python
module, but xcb-proto is very low in the build to force a dependency on
python-native.
As it turns out libxcb simply asks pkg-config for the full path to the module
xcb-proto installed and uses it directly so there is no need to build
python-native. Instead replace AM_PATH_PYTHON with two explicit variable
definitions (need to set PYTHON for automake's install logic).
Also remove the dependency on xcb-proto-native as libxcb uses the data files and
tooling from the target sysroot, and patching it to use the native sysroot adds
complication for no good reason.
Signed-off-by: Ross Burton <ross.burton@intel.com>
