Remove some now-incorrect and now-obsolete DCHECKs.

~Mutex already checks that the mutex isn't locked, and already has an
exception for the case where we're shutting down.

Change-Id: Ide2343fb5fe06ee8a5014023bc1817ec142e5ec8
diff --git a/src/monitor.cc b/src/monitor.cc
index a29f2a1..c4deccb 100644
--- a/src/monitor.cc
+++ b/src/monitor.cc
@@ -123,13 +123,6 @@
 Monitor::~Monitor() {
   DCHECK(obj_ != NULL);
   DCHECK_EQ(LW_SHAPE(*obj_->GetRawLockWordAddress()), LW_SHAPE_FAT);
-
-#ifndef NDEBUG
-  // This lock is associated with an object that's being swept.
-  bool locked = lock_.TryLock();
-  DCHECK(locked) << obj_;
-  lock_.Unlock();
-#endif
 }
 
 /*