Fix hang in cache copyobject call (#8993)

Avoid GetObjectNInfo call from cache in CopyObjectHandler
- in the case of server side copy with metadata replacement,
the reader returned from cache is never consumed, but the net
effect of GetObjectNInfo from cache layer, is cache holding a
write lock to fill the cache. Subsequent stat operation on cache in
CopyObject is not able to acquire a read lock, thus causing the hang.

Fixes #8991

cmd/object-handlers.go

@@ -812,9 +812,6 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 	cpSrcDstSame := isStringEqual(pathJoin(srcBucket, srcObject), pathJoin(dstBucket, dstObject))
 
 	getObjectNInfo := objectAPI.GetObjectNInfo
-	if api.CacheAPI() != nil {
-		getObjectNInfo = api.CacheAPI().GetObjectNInfo
-	}
 
 	var lock = noLock
 	if !cpSrcDstSame {