deprecate and remove old "scope=None" logic for scoped_session()

[Mike Bayer]

some old cruft that should be removed in https://github.com/zzzeek/sqlalchemy/pull/307/files within scoped_session call(), source is very old commit b8b51fe4379936fe142c875ea0f17da14a12c27d. nevertheless, this is non-underscored so someone might be using it.

[Mike Bayer]

googling and looking in stackoverflow reveals that even very old tutorials regarding scoped_session() make no mention of this keyword, which appears to never have been documented. going to remove it in 1.2.

[Mike Bayer]

Remove "scope" keyword from scoped_session.call()

Removed a very old keyword argument from :class:.scoped_session called scope. This keyword was never documented and was an early attempt at allowing for variable scopes.

Change-Id: I9a26498a1a66d1eafb0723e98b527688a60f9d9b Fixes: #3796

→ <<cset 1a08c41048ef>>