Remove unused variable.

Reviewed by: cognet

lib/libthr/arch/arm/arm/pthread_md.c

@@ -32,10 +32,6 @@
 
 #include "pthread_md.h"
 
-struct umtx arm_umtx = {
-	.u_owner = UMTX_UNOWNED
-};
-
 struct tcb *
 _tcb_ctor(struct pthread *thread, int initial)
 {

lib/libthr/arch/arm/include/pthread_md.h

@@ -35,9 +35,6 @@
 #include <sys/types.h>
 #include <machine/sysarch.h>
 #include <stddef.h>
-#include <errno.h>
-
-#include <sys/umtx.h>
 
 #define	DTV_OFFSET		offsetof(struct tcb, tcb_dtv)
 
@@ -83,6 +80,4 @@ _get_curthread(void)
 	return (NULL);
 }
 
-extern struct umtx arm_umtx;
-
 #endif /* _PTHREAD_MD_H_ */