Make wxPG_FLOAT_PRECISION a built-in wxFloatProperty attribute

wxPG_FLOAT_PRECISION value is used only internally in wxFloatProperty and there is no need to make it readable via getter function.

src/propgrid/props.cpp

@@ -1038,16 +1038,6 @@ bool wxFloatProperty::DoSetAttribute( const wxString& name, wxVariant& value )
     return false;
 }
 
-wxVariant wxFloatProperty::DoGetAttribute( const wxString& name ) const
-{
-    wxVariant value;
-    if ( name == wxPG_FLOAT_PRECISION )
-    {
-        value = (long)m_precision;
-    }
-    return value;
-}
-
 wxValidator*
 wxFloatProperty::GetClassValidator()
 {