auth: Use deb-conffiles mechanism to remove old conffiles

[zeha]

Short description

Switches Debian packaging for authoritative server from a custom preinst script to the dpkg-supported way of removing old conffiles. This feature is available since dpkg 1.20.6 (in Debian bullseye).

Might help Debian users with sysvinit.

I've put the same change into Debian's packaging, minus the Pre-Depends, as I don't expect Debian's packaging to be reused by anyone for EOL releases.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[zeha]

So it turns out, the official dpkg support for this is nothing better than our custom script:

Unpacking pdns-server (4.9.3-2) ...
Obsolete conffile '/etc/init.d/pdns' has been modified by you.
Saving as /etc/init.d/pdns.dpkg-old ...

[zeha]

Depending on how far back you want to support upgrades, we could also just drop it altogether.

[coveralls]

Pull Request Test Coverage Report for Build 12856930539

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 31 unchanged lines in 8 files lost coverage.
• Overall coverage increased (+0.01%) to 64.706%

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Files with Coverage Reduction	New Missed Lines	%
pdns/recursordist/sortlist.cc	2	74.12%
pdns/backends/gsql/gsqlbackend.hh	2	97.71%
modules/lmdbbackend/lmdbbackend.cc	2	73.62%
pdns/packethandler.cc	3	72.44%
pdns/remote_logger.cc	3	53.81%
pdns/iputils.cc	3	56.07%
pdns/opensslsigners.cc	3	61.34%
pdns/recursordist/test-syncres_cc1.cc	13	89.41%

Totals
Change from base Build 12832418127:	0.01%
Covered Lines:	127803
Relevant Lines:	166436

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💛 - Coveralls