Remove TARGET_PROJECT[_SYSTEM]_INCLUDES

Everything should be getting device specific kernel headers from the
device_kernel_headers header library these days.

This does change the behavior of system libraries on devices using the
VNDK -- they no longer get device-specific kernel headers by default, as
we generally expect the system image to be device-independent. The few
libraries that may still need this can use:

 LOCAL_HEADER_LIBRARIES += device_kernel_headers

Test: treehugger
Change-Id: I90ccb921d58b8d27dd0118a974202696e0af745f