meson: drop leftover PTHREAD_SETAFFINITY_IN_NP_HEADER

55765f80 replaced this with a check for the header itself.

Fixes: 55765f80b9ce7cce4ec6 ("util/u_thread: include pthread_np.h if found")
Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Jonathan Gray <jsg@jsg.id.au>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6548>
1 file changed