Avoid dh_missing warnings when building the debian package

Summary:
The dh_missing helper checks that all the files from the tmp directory
have an installation rule. Otherwise:

• With compat level < 12: it silently ignores the files
• With compat level 12: it warns about the presence of these files
• With compat level > 12: it errors out in the presence of these files

This diff improves our build wrt dh_missing by avoiding putting files
to the tmp directory which are not installed (namely the
bitcoinconsensus library and the seeder), and enforce dh_missing to
raise a warning if some files remain. It doesn't change the current
behavior since we are using compat level 12 but will prevent future
builds from failing if this level is bumped.

Test Plan:
See the build log in Launchpad and check there is no warning anymore:
https://launchpadlibrarian.net/500304852/buildlog_ubuntu-focal-amd64.bitcoinabc_0.22.4.5-focal_BUILDING.txt.gz

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7733