Fix rubocop error

lib/neo4j/node.rb

@@ -118,16 +118,11 @@ def del
       fail 'not implemented'
     end
 
-    # @return true if the node exists in the database
+    # @return [Boolean] true if the node exists in the database
     def exist?
       fail 'not implemented'
     end
 
-    # @return all the Neo4j labels for this node
-    def labels
-      fail 'not implemented'
-    end
-
     # Returns the only node of a given type and direction that is attached to this node, or nil.
     # This is a convenience method that is used in the commonly occuring situation where a node has exactly zero or one relationships of a given type and direction to another node.
     # Typically this invariant is maintained by the rest of the code: if at any time more than one such relationships exist, it is a fatal error that should generate an exception.
@@ -160,11 +155,6 @@ def rel?(spec = {})
       fail 'not implemented'
     end
 
-    # @return [Boolean] true if the node exists
-    def exist?
-      fail 'not implemented'
-    end
-
     # Works like #rels method but instead returns the nodes.
     # It does try to load a Ruby wrapper around each node
     # @abstract