Deprecate validateOptions

[kentcdodds]

There's even an example using this API, however it starts with:

NOTE: It is recommended to now use the apiCheck property instead of validateOptions.

The validateOptions api was created before angular-formly adopted api-check wholesale. I think that api-check is the correct way to validate custom types and therefore don't see the value of validateOptions anymore. Anyone opposed to me deprecating that api and removing it in the next release?

[kentcdodds]

I think that I'll start with a deprecation notice for this one. Then in 7.0.0, I'll rip it out altogether.