fix metadata requirement in fk render; remove column.copy()

fix metadata requirement in fk render; remove column.copy()

Fixed autogenerate rendering bug which failed to render foreign key
constraints local to a :class:`.CreateTableOp` object if it did not refer
to a ``MetaData`` collection via a private constructor argument that would
not ordinarily be passed in user-defined rewriter recipes, including ones
in the Alembic cookbook section of the docs.

Also removed the use of column.copy() from the CreateTableOp rewriter
recipe and added a new test for this recipe which includes a table with
an FK.  it's not clear why copy() was needed here and if we get more
reports of issues, we can add to this test suite and adjust.

Fixes: #1692
Change-Id: I6cf6c8f62b7eb116cfc78216b3dbcbddad499691