Vote entity unnecessarily re-implements features provided by base class

Added related issue to link the core issue where ContentEntityBase acquired these base fields.

Correct me if I'm wrong, but when comparing the old code to that of the ContentEntityBase, I don't think there are actually any database changes needed. Of course, this will need to be tested - I am currently waiting on a conversion script to turn ~330.000 flags into votes, I guess that should be sufficient - but I am just wondering if I am overlooking something.

tr → changed the visibility of the branch 8.x-3.x to hidden.

tr → changed the visibility of the branch 3153550-vote-entity-unnecessarily to hidden.

tr → changed the visibility of the branch 4.0.x to hidden.

tr → closed merge request !30

tr → closed merge request !31

tr → changed the visibility of the branch 3153550-vote-entity to active.

tr → changed the visibility of the branch 3153550-vote-entity to hidden.

I screwed up the issue fork by trying to rebase the changes into 4.0.x. Maybe someone can fix that - I've tried all the simple things and am unwilling to spend more time on it.

So right now I will be relying on the patch instead. Here is a manual re-roll against 4.0.x.

tr → changed the visibility of the branch 3153550-vote-entity-unnecessarily to active.