[#411] Remove unnecessary pointers for sync objects

Signed-off-by: Alejandro Lopez <a.lopez@yadro.com>

cmd/frostfs-node/cache.go

@@ -25,19 +25,18 @@ type valueWithTime[V any] struct {
 }
 
 type locker struct {
-	mtx     *sync.Mutex
+	mtx     sync.Mutex
 	waiters int // not protected by mtx, must used outer mutex to update concurrently
 }
 
 type keyLocker[K comparable] struct {
 	lockers    map[K]*locker
-	lockersMtx *sync.Mutex
+	lockersMtx sync.Mutex
 }
 
 func newKeyLocker[K comparable]() *keyLocker[K] {
 	return &keyLocker[K]{
-		lockers:    make(map[K]*locker),
-		lockersMtx: &sync.Mutex{},
+		lockers: make(map[K]*locker),
 	}
 }
 
@@ -53,7 +52,6 @@ func (l *keyLocker[K]) LockKey(key K) {
 	}
 
 	locker := &locker{
-		mtx:     &sync.Mutex{},
 		waiters: 1,
 	}
 	locker.mtx.Lock()