CodeAssist: The correction is just used inside C++ proposal.

Adding an empty default implementation to the base and
Removing boilerplate code from the specialized classes.

Change-Id: I4469d9f05d2ff153c0867c10683f86b4f656fd3d
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/texteditor/codeassist/iassistproposal.cpp

@@ -93,12 +93,22 @@ int IAssistProposal::basePosition() const
     is displayed.
 */
 
+bool IAssistProposal::isCorrective() const
+{
+    return false;
+}
+
 /*!
     \fn void TextEditor::IAssistProposal::makeCorrection(BaseTextEditor *editor)
 
     This allows a correction to be made in the case this is a corrective proposal.
 */
 
+void IAssistProposal::makeCorrection(TextEditorWidget *editorWidget)
+{
+    Q_UNUSED(editorWidget);
+}
+
 /*!
     \fn IAssistModel *TextEditor::IAssistProposal::model() const