In Linux kernel commit 819fbd3d8ef36c09576c2a0ffea503f5c46e9177
these two header files were moved to staging (though they've since
been moved out again by Linus.)
We do not actually use this, and it's in a state of maybe-removal
from the kernel as of Linux 5.14. Get rid of it; mpv still builds
fine without it, so it wasn't needed anyways.
Fixes#9233.