Removes duplicate indexes from activities migration template

[adamkiczula]

I noticed in my app that I had duplicate indexes. As of rails/rails#23179, using belongs_to or references automatically adds an index. #64 previously manually added the indexes, but they are no longer needed.

[bhtabor]

Thank you @adamkiczula! I think this should be merged to avoid unnecessary redundant indexes.

[ur5us]

Thanks @adamkiczula. Will take a look in the next few days.

[adamkiczula]

Thanks, I learned recently that with this change Rails actually defaults to type, id for the index, which I believe is less optimal in some cases (but more optimal if you're querying just by type). Just pointing out that the two aren't equivalent, an alternative would be to disable Rails' default index in the template. Or maybe just pick one, but add a comment informing the user explaining and they can modify based on their use case?

[bhtabor]

Rails actually defaults to type, id for the index, which I believe is less optimal in some cases (but more optimal if you're querying just by type).

Good point. I think querying just by type is much more common than just by id though. Rails default is probably enough here.