Don't remove syntax errors on each document change

Especially when several error markers exist, the flashing this causes
while editing isn't really nice.

Reviewed-by: Roberto Raggi

src/plugins/cpptools/cppmodelmanager.cpp

@@ -717,8 +717,6 @@ void CppModelManager::onDocumentUpdated(Document::Ptr doc)
                     continue;
                 else if (lines.contains(m.line()))
                     continue;
-                //else if (lines.size() == MAX_SELECTION_COUNT)
-                    //break; // we're done.
 
                 lines.insert(m.line());
 

src/plugins/cpptools/cppmodelmanager.h

@@ -168,10 +168,6 @@ private:
 
     mutable QMutex mutex;
 
-    enum {
-        MAX_SELECTION_COUNT = 5
-    };
-
     struct Editor {
         QPointer<TextEditor::BaseTextEditor> widget;
         QList<QTextEdit::ExtraSelection> selections;

src/plugins/cpptools/cpptoolseditorsupport.cpp

@@ -91,10 +91,6 @@ void CppEditorSupport::updateDocument()
         const QList<QTextEdit::ExtraSelection> selections =
                 edit->extraSelections(TextEditor::BaseTextEditor::CodeWarningsSelection);
 
-        if (! selections.isEmpty())
-            edit->setExtraSelections(TextEditor::BaseTextEditor::CodeWarningsSelection,
-                                     QList<QTextEdit::ExtraSelection>());
-
         _modelManager->stopEditorSelectionsUpdate();
     }