Don't use and_() inside of Query.filter_by

Don't use and_() inside of Query.filter_by

Adjusted the :meth:`.Query.filter_by` method to not call :func:`.and()`
internally against multiple criteria, instead passing it off to
:meth:`.Query.filter` as a series of criteria, instead of a single criteria.
This allows :meth:`.Query.filter_by` to defer to :meth:`.Query.filter`'s
treatment of variable numbers of clauses, including the case where the list
is empty.  In this case, the :class:`.Query` object will not have a
``.whereclause``, which allows subsequent "no whereclause" methods like
:meth:`.Query.select_from` to behave consistently.

Fixes: #4606
Change-Id: Ifc8cdbf13accca2236068ef70114a7c35ab159ff