* [chore] Remove go-playground/validator
It turns out we're not actually using the validator code. This is a
remnant from when we intended to use it, but the presence of it and its
struct tags creates the illusion we're validating a lot of things we're
not. It resulted in some confusion when we were trying to figure out
language valdiation.
Remove all this code, so that only the validation functions from the
validate package we actually use remain. I'm not touching the struct
tags in the migrations in order to avoid things potentially thinking
migrations need to be re-run.
* [chore] Bring back a struct tag on api
The validate on internal/api is Gin doing form validation, not the
validator from go-playground/validator.
