Revert "sched.h needs to be imported on Darwin/OSX targets."

This reverts commit 9dc5063262.

This breaks the build on at least Linux, probably other non-apple
platforms.

Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>

src/gallium/drivers/swr/swr_fence.cpp

@@ -29,10 +29,6 @@
 #include "swr_screen.h"
 #include "swr_fence.h"
 
-#ifdef __APPLE__
-#include <sched.h>
-#endif
-
 #if defined(PIPE_CC_MSVC) // portable thread yield
    #define sched_yield SwitchToThread
 #endif