Remove client-side password crypto from JS tests

This removes client-side password crypto from the JavaScript tests.

In some JavaScript tests, it has been assumed that SHA-1 is used for the
password hash in user docs.  Those tests should, however, not rely on
implementation details of the user authentication hash function, as it
isn't the goal of those tests to check these.  Furthermore, this causes
problems when a password scheme is changed, or a new one is introduced.

This work clears the way for solving COUCHDB-1780 (upgrade users
password hash on login).  When a mechanism for upgrading user docs to a
newer password scheme is being introduced, this change will prevent
problems with tests that would fail because they'd be relying on an old
password scheme.