Don't require request to contain google_id.

This information is embedded in the ID token already as the sub field.
All flows in OpenID Connect Core 1.0 specify that the token should
be validate then the Subject Identifier should be retrieved.

Subject Identifier is not involved in the validtion process according
to section 3.1.3.7:
http://openid.net/specs/openid-connect-core-1_0.html#IDTokenValidation