Fixes Issue #2391 - Remove sqlx features from db_pools

[aadityadhruv]

By removing sqlx features from the crate itself, the choice is put upon the user, which lets them choose between rustls and native-tls.

[SergioBenitez]

Remove the feature means that sqlx doesn't compile. Not removing the feature means we have this issue. Adding a separate feature to enable native_tls instead means we can't compile the crate with --all-features. I don't see a solution here that is good. The problems, in my opinion, are in sqlx (for how they implemented features, which they've fixed in 0.7) and rustls/webpki, for the initial source of the problem with resolving IP addresses.

I am unfortunately inclined to suggest that we wait for a fix upstream. Unless there's a solution I'm missing that:

1. Doesn't require everyone to depend on sqlx for use db_pools with sqlx.
2. Allowing use to build contrib with --all-features.
3. Allows selecting either rustls or native-tls

[aadityadhruv]

That sounds good to me!