Remove unused code

lib/models/documents/document.dart

@@ -118,7 +118,7 @@ class Document {
     return block.queryChild(res.offset, true);
   }
 
-  compose(Delta delta, ChangeSource changeSource, {bool history}) {
+  compose(Delta delta, ChangeSource changeSource) {
     assert(!_observer.isClosed);
     delta.trim();
     assert(delta.isNotEmpty);

lib/models/documents/history.dart

@@ -88,7 +88,7 @@ class History {
     dest.add(inverseDelta);
     this.lastRecorded = 0;
     this.ignoreChange = true;
-    doc.compose(delta, ChangeSource.LOCAL, history: true);
+    doc.compose(delta, ChangeSource.LOCAL);
     this.ignoreChange = false;
   }