MAINTAINERS: Remove dead path from LOCKING PRIMITIVES entry

Since 890658b7ab48 ("locking/mutex: Kill arch specific code"), there
are no mutex header files under arch/, so we can remove the redundant
entry from MAINTAINERS.

Reported-by: Joe Perches <joe@perches.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Cc: Jason Low <jason.low2@hpe.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181001142856.GC9716@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

MAINTAINERS

@@ -8598,7 +8598,6 @@ F:	include/linux/spinlock*.h
 F:	arch/*/include/asm/spinlock*.h
 F:	include/linux/rwlock*.h
 F:	include/linux/mutex*.h
-F:	arch/*/include/asm/mutex*.h
 F:	include/linux/rwsem*.h
 F:	arch/*/include/asm/rwsem.h
 F:	include/linux/seqlock.h