Tear down code for phone profile verification

[jmhooper]

Why: The phone verification process for IdV used to mirror USPS
verification. We changed that functionality, but never properly cleaned
up some of the dead code. This commit does that, and also prepares to
drop the unnecessary phone_confirmed column from the profile model.

Hi! Before submitting your PR for review, and/or before merging it, please
go through the following checklist:

• For DB changes, check for missing indexes, check to see if the changes
  affect other apps (such as the dashboard), make sure the DB columns in the
  various environments are properly populated, coordinate with devops, plan
  migrations in separate steps.

• For route changes, make sure GET requests don't change state or result in
  destructive behavior. GET requests should only result in information being
  read, not written.

• For encryption changes, make sure it is compatible with data that was
  encrypted with the old code.

• For secrets changes, make sure to update the S3 secrets bucket with the
  new configs in all environments.

• Do not disable Rubocop or Reek offenses unless you are absolutely sure
  they are false positives. If you're not sure how to fix the offense, please
  ask a teammate.

• When reading data, write tests for nil values, empty strings,
  and invalid formats.

• When calling redirect_to in a controller, use _url, not _path.

• When adding user data to the session, use the user_session helper
  instead of the session helper so the data does not persist beyond the user's
  session.

• When adding a new controller that requires the user to be fully
  authenticated, make sure to add before_action :confirm_two_factor_authenticated.

[jmhooper]

This commit tears out the unused code. I'd like to go back and move the profile verification logic into the IdV namespace and pull out some of the branching. That seemed like it would add too much bloat to this PR so I'm going to hold off for now.

[jmhooper]

I'm confused about why code climate is saying coverage has decreased? It's telling me it's gone down in the VerifyProfilePhoneController, which is a file I deleted.

[jmhooper]

The code coverage check here looks like it is failing since I deleted a whole bunch of covered code, reducing the total code coverage percentage. I don't think I introduced any uncovered paths.

[jgsmith-usds]

It's expected for the ratio to decrease if we subtract the same number from the numerator and denominator (e.g., all lines of code removed were covered).

[monfresh]

LGTM. I love code removals.