Removing transition stuff in debhelper scripts after which time?

[Daniel Leidert <daniel.leidert.spam@gmx.net>]

Hi,

Today I stumbled over the question: After which time should transition
stuff be removed from the debhelper scripts. In this special case I'm
talking about install-sgmlcatalog calls in (e.g.) postinst scripts. Adam
Di Carlo announced the depreciation of install-sgmlcatalogs in 2001.
However, almost all related docbook* packages still contain this stuff.
So I'm wondering, how long one should wait before such obsolete stuff
can be removed? I mean, there is no requirement to support updates from
e.g. Woody to Lenny, right? I checked the Debian Social Contract and the
Policy manuals, but didn't find an information related to this topic.
Maybe I overlooked it?

Regards, Daniel