Remove Applicative#traverse and Applicative#sequence

[LukaJCB]

These don't really serve any purpose and just delegate to the functions on Traverse so let's get rid of them.

[travisbrown]

As a little extra motivation, if you try to call traverse on something like catsStdInstancesForVector with type parameters, the compiler will complain about the middle parameter not having the right kind (because of the collision between Applicative#traverse and Traverse#traverse). You can easily work around this by upcasting the instances, but it's still vaguely annoying.

[kubukoz]

I think I can make this happen ;) always calling dibs on removing some code

[jtjeferreira]

If anyone is missing the Applicative#sequence when use in a composed Applicative like in Applicative[Future].compose[MyValidatedNel].sequence(segments), then an workaround described in
https://gitter.im/typelevel/cats?at=5a564e2f232e79134dedaad5