Issue #1980 - Fix build bustage for applications where WebRTC building is enabled.

Turns out we have a duplicate VoidFunction callback in the WebIDLs. Per
 Mozilla bug 1324169, we should remove this callback from
 RTCPeerConnection.webidl and let Function.webidl handle it instead.
The AttributeError faced by the new Basilisk dev wasn't helpful at all;
 and turns out Mozilla had this exact same issue on bug 1505504. We're
 also backporting that just in case we encounter another case of
 callback duplication.
Also doing a minor fix in the MicroTaskRunnable class which Moonchild
 forgot to do while working on Issue #1895.

dom/bindings/parser/WebIDL.py

@@ -248,8 +248,14 @@ class IDLScope(IDLObject):
         return self.QName()
 
     def QName(self):
-        if self._name:
-            return self._name.QName() + "::"
+        # It's possible for us to be called before __init__ has been called, for
+        # the IDLObjectWithScope case.  In that case, self._name won't be set yet.
+        if hasattr(self, "_name"):
+            name = self._name
+        else:
+            name = None
+        if name:
+            return name.QName() + "::"
         return "::"
 
     def ensureUnique(self, identifier, object):

xpcom/base/CycleCollectedJSContext.h

@@ -142,7 +142,7 @@ public:
   virtual void Run(AutoSlowOperation& aAso) = 0;
   virtual bool Suppressed() { return false; }
 protected:
-  virtual ~MicroTaskRunnable() {}
+  virtual ~MicroTaskRunnable() = default;
 };
 
 class CycleCollectedJSContext