staging: lustre: remove libcfs_debug_set_level prototype from libcfs_private.h

The function libcfs_debug_set_level is used only internally so no reason
to expose it in libcfs_private.h. This is broken out from LU-5829 patch
http://review.whamcloud.com/13319.
Signed-off-by: frank zago <fzago@cray.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/include/linux/libcfs/libcfs_private.h

@@ -185,8 +185,6 @@ int libcfs_debug_cleanup(void);
 int libcfs_debug_clear_buffer(void);
 int libcfs_debug_mark_buffer(const char *text);
 
-void libcfs_debug_set_level(unsigned int debug_level);
-
 /*
  * allocate per-cpu-partition data, returned value is an array of pointers,
  * variable can be indexed by CPU ID.