Don't plot private symbol text.

Fixes https://gitlab.com/kicad/code/kicad/issues/11548

eeschema/lib_symbol.cpp

@@ -625,6 +625,10 @@ void LIB_SYMBOL::Plot( PLOTTER* aPlotter, int aUnit, int aConvert, bool aBackgro
 
     for( const LIB_ITEM& item : m_drawings )
     {
+        // Do not plot private items
+        if( item.IsPrivate() )
+            continue;
+
         // Lib Fields are not plotted here, because this plot function
         // is used to plot schematic items, which have they own fields
         if( item.Type() == LIB_FIELD_T )

eeschema/lib_text.cpp

@@ -263,6 +263,9 @@ void LIB_TEXT::Plot( PLOTTER* plotter, bool aBackground, const VECTOR2I& offset,
 {
     wxASSERT( plotter != nullptr );
 
+    if( IsPrivate() )
+        return;
+
     if( aBackground )
         return;