While at it, also relinquish active commit rights:
[x years between commits] is probably a poster child example of inactivity :)
Signed-off-by: NEric Blake <eblake@redhat.com>

Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

Signed-off-by: NGao feng <gaofeng@cn.fujitsu.com>

And Guannan Ren who was missing from the list

AUTHORS.in tracks the maintainers, as well as some folks who were
previously in AUTHORS but don't have a git commit with proper
attribution.

Generated output is sorted alphabetically and lacks pretty spacing, so
tweak AUTHORS.in to follow the same format.

Additionally, drop the syntax-check rule that previously validated
AUTHORS against git log.