Clear NEW flags after import.

Fixes https://gitlab.com/kicad/code/kicad/issues/8750

eeschema/sch_plugins/altium/sch_altium_plugin.cpp

@@ -235,6 +235,7 @@ SCH_SHEET* SCH_ALTIUM_PLUGIN::Load( const wxString& aFileName, SCHEMATIC* aSchem
 
     SCH_SCREENS allSheets( m_rootSheet );
     allSheets.UpdateSymbolLinks(); // Update all symbol library links for all sheets.
+    allSheets.ClearEditFlags();
 
     return m_rootSheet;
 }

eeschema/sch_screen.cpp

@@ -1246,6 +1246,16 @@ int SCH_SCREENS::ReplaceDuplicateTimeStamps()
 }
 
 
+void SCH_SCREENS::ClearEditFlags()
+{
+    for( SCH_SCREEN* screen = GetFirst(); screen; screen = GetNext() )
+    {
+        for( SCH_ITEM* item : screen->Items() )
+            item->ClearEditFlags();
+    }
+}
+
+
 void SCH_SCREENS::DeleteMarker( SCH_MARKER* aMarker )
 {
     for( SCH_SCREEN* screen = GetFirst(); screen; screen = GetNext() )

eeschema/sch_screen.h

@@ -613,6 +613,8 @@ public:
      */
     void UpdateSymbolLinks( REPORTER* aReporter = nullptr );
 
+    void ClearEditFlags();
+
     /**
      * Test all of the schematic symbols to see if all #LIB_ID objects library nickname is not
      * set.