Removing obsolete features for the 1.15.x series

[Guillem Jover <guillem@debian.org>]

Hi!

While checking the remaining stuff to be done prior to the next release,
I thought we could do a round of removals before the 1.15 series hit
unstable.

So if no one sees any problem, I'll remove the following from the
items listed on README.feature-removal-schedule:

  * 822-date (all filed bugs have been fixed)
  * Obsolete priorities
  * Obsolete dpkg otions (all of them)


Then after having thought for a bit about the deprecated support for
substvars in dpkg-source and dpkg-genchanges (due to 526132), I've
changed my mind. Even if there's no use at all for substvars or they
are (currently) undesirable making the source not easily reproducible,
for Debian and most derivatives using the same build processesor, I
think it might be interesting for uses like templated source package
generation and similar, or other interesting ideas we might not have
thought about.

Also the same logic we apply for the removal of the substvar support
could be applied to most of the “Build options” as well, as those do
not make sense in the normal build for official packages (like -U, or
-D). So if no one sees any problem I'd like to revert back the status
for this from deprecated to supported.

regards,
guillem