Reverting 'Two-factor authentication' support as it cause OSX and docker build failures.

This reverts commit 787a441343.

web/pgadmin/model/__init__.py

@@ -473,11 +473,3 @@ class UserMacros(db.Model):
     )
     name = db.Column(db.String(1024), nullable=False)
     sql = db.Column(db.Text(), nullable=False)
-
-
-class UserMFA(db.Model):
-    """Stores the options for the MFA for a particular user."""
-    __tablename__ = 'user_mfa'
-    user_id = db.Column(db.Integer, db.ForeignKey(USER_ID), primary_key=True)
-    mfa_auth = db.Column(db.String(64), primary_key=True)
-    options = db.Column(db.Text(), nullable=True)