Remove unneeded migrations

[gazayas]

These migrations can be found 1-for-1 in the starter repository, so I don't think we need them here in the core repository.

I did not delete migrations for bullet_train-outgoing_webhooks because we need those for the tests.

Besides that I almost skipped over bullet_train-integrations-stripe because I thought we would need the migrations, but I was thinking of bullet_train-billing-stripe (The following is from the documentation).

2.3. Copy Database Migrations

Use the following two commands on your shell to copy the required migrations into your local project:

cp `bundle show --paths | grep bullet_train-billing | sort | head -n 1`/db/migrate/* db/migrate
cp `bundle show --paths | grep bullet_train-billing-stripe | sort | head -n 1`/db/migrate/* db/migrate

Totally understandable if this is too much in one PR, just let me know if you want me to split it up or take another approach.

[jagthedrummer]

I didn't even realize these files where there. I think removing them seems safe.

@pascallaliberte @kaspth @andrewculver Do you guys have any concerns with this?

[kaspth]

Do we still want to support non-Bullet Train apps being able to use any of these libraries by themselves? That's my only concern, though I'm not sure if removing these migrations will affect that.

Other than that, since these are already in the starter repo, I think we can safely remove them.

[jagthedrummer]

🤔 Hmmm... that's a really good point about the migrations potentially being useful for non-starter-repo apps.