Move testasyncgetprop.c to x11/
window: Remove support for _NET_WM_ICON_NAME

We don't seem to use it anywhere.
Remove x11/ directory from default include path
Don't include wayland/ by default either
Move session to x11/

XSMP code is X11-specific, of course.
Don't generate sources in a subdirectory

This fixes srcdir != builddir issues.