Nuke the pkg 'infos' stuff -- it's unused and obsoleted by pkg
annotate.
Nuke PKG_INFOS from orbit (it's the only way to be sure.)

'infos' is almost entirely unused, and is hereby deprecated.  Use pkg
attribute instead.

The 'infos' attribute field in struct pkg has been deleted.

The database schema for the packages table has been altered to remove
the infos column.  Any pre-existing 'infos' data will be converted into
a pkg annotation tagged as '_INFOS_'

YAML nodes tagged as 'infos' will be converted into pkg annotations
tagged by '_INFOS_' on input.  YAML nodes tagged as 'infos' will not
be emitted on output.

Drop the %i format code for pkg_printf()

Derive the number of attr fields in struct pkg automatically from the
pkg_attr enum.  Also, start counting the enum values from zero, as
they are used as array indices, and C arrays start from index zero.
This reduces the number attr fields in struct pkg by *two* as field 0
was never previously used.

TODO: drop 'infos' handling entirely from pkg manifest at the next
major version bmp.