[core] Graph: avoid double update while adding/removing an edge

Graph.markNodesDirty() is called in three different places:
- Attribute.requestGraphUpdate()
- Graph.addEdge()
- Graph.removeEdge()

However, addEdge() and removeEdge() are especially decorated to request a graph update so, with the old markNodesDirty() implementation, the update was done twice in a row.

meshroom/core/attribute.py

@@ -142,6 +142,7 @@ class Attribute(BaseObject):
     def requestGraphUpdate(self):
         if self.node.graph:
             self.node.graph.markNodesDirty(self.node)
+            self.node.graph.update()
 
     @property
     def isOutput(self):

meshroom/core/graph.py

@@ -1059,7 +1059,7 @@ class Graph(BaseObject):
 
     def markNodesDirty(self, fromNode):
         """
-        Mark all nodes following 'fromNode' as dirty, and request a graph update.
+        Mark all nodes following 'fromNode' as dirty.
         All nodes marked as dirty will get their outputs to be re-evaluated
         during the next graph update.
 
@@ -1072,7 +1072,6 @@ class Graph(BaseObject):
         nodes, edges = self.nodesFromNode(fromNode)
         for node in nodes:
             node.dirty = True
-        self.update()
 
     def stopExecution(self):
         """ Request graph execution to be stopped by terminating running chunks"""