Remove native data from RealItem

It seems that native data is used as a backup of the data. In RealItem::updateToInstrument we can see that data:=native_data if to unlink instrument.

changed milestone to %20 GUI refactoring

added simplify label

changed the description

added GUI label

removed milestone %20 GUI refactoring

marked this issue as related to #320 (closed)

marked this issue as related to #69 (closed)

marked this issue as related to #621 (closed)

added linked to meta label

assigned to @m.svechnikov

mentioned in merge request !2179 (merged)

mentioned in commit e7448a4c

closed with merge request !2179 (merged)