Feature/issue 652 remove nesterov optimization

#### Summary:

Removes Nesterov optimization from Stan.


#### Intended Effect:

Removes Nesterov optimization.

#### How to Verify:

Run the unit test. The history shows that there were 4 parameters and now there are 3.

#### Side Effects:

This will affect CmdStan, RStan, and PyStan. I'll add new issues to each of them after this pull request is incorporated.

#### Documentation:

Documentation will need to be updated in CmdStan, RStan, and PyStan.

#### Reviewer Suggestions:

Anyone.