Get rid of all deprecated code before 1.0 release

[volovyks]

We should delete all the code that was deprecated at least 3 months ago before naj 1.0.0 release.

Bonus points for deprecating code in other places, like this one: https://github.com/near/near-api-js/blob/master/src/utils/serialize.ts#L3

[zurgl]

@volovyk-s Hey, if no one is currently working on it, may be i can help sparing my free time on this.
Let me know

[volovyks]

Hey @zurgl! Thank you, we always need some help.
You can work on this issue, but we will merge it only before the 1.0 release. So there is a risk of conflicts.
Check this one: near/near-cli#751
If you are interested - post a comment there and I will assign you.

[zurgl]

@volovyk-s The related issue have already been assigned and link to a PR almost completed. When the 1.0 release his expected to occur ?

[volovyks]

Currently, I'm focused on NEAR CLI.
If you want to work on near-api-js - here is a great ticket to work on: #627