[XFS] Remove unused tracing code

None of this code appears to be used anywhere so remove it.
Reviewed-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

fs/xfs/xfs_inode.c

@@ -3232,8 +3232,6 @@ corrupt_out:
 
 
 #ifdef XFS_ILOCK_TRACE
-ktrace_t	*xfs_ilock_trace_buf;
-
 void
 xfs_ilock_trace(xfs_inode_t *ip, int lock, unsigned int lockflags, inst_t *ra)
 {

fs/xfs/xfs_inode.h

@@ -223,7 +223,6 @@ struct xfs_dquot;
 
 #if defined(XFS_ILOCK_TRACE)
 #define XFS_ILOCK_KTRACE_SIZE	32
-extern ktrace_t *xfs_ilock_trace_buf;
 extern void xfs_ilock_trace(struct xfs_inode *, int, unsigned int, inst_t *);
 #else
 #define	xfs_ilock_trace(i,n,f,ra)