revlog: no longer return sidedata from `_revisiondata`
All users have been migrated.
When they was introduced sidedata where grouped with the actual revision data
and unpacking one came with the other. Sidedata moved be stored "independently"
and it no longer make sense to retrieve both at the same time unconditionnaly.
Differential Revision: https://phab.mercurial-scm.org/D10783
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true