Remove dependency on V2Authenticator from ThirdParty and pairing authenticators.
Previously third-party and pairing authenticators were responsible for
creation for the underlying SPAKE2 authenticators. Now they get a
callback that they should use instead. This will allow to use them with
Spake2Authenticator.
Also made some minor cleanups in pairiting authenticators, particularly
in the code responsible for fetching the pin after paired auth fails.
BUG=589698
Review URL: https://codereview.chromium.org/1770923002
Cr-Commit-Position: refs/heads/master@{#379858}
16 files changed
