remove libevent and libpcre2 packages

[sssoleileraaa]

Status

Ready for review
Closes freedomofpress/securedrop#5312

Description of changes

Removed upgrade-path dependency packages, libevent and libpcre2, now that we no longer provide an upgrade path from 1.2.2 with the release of SecureDrop 1.5.0.

Test plan

Once this PR is merged, reprepro will automatically run and update the apt server metadata (and also automatically sign the release file with the apt-tst key) so that the packages are no longer on our apt-test server. To test this, wait about 10-20 minutes before checking that:

• libevent1 is no longer available here: https://apt-test.freedom.press/pool/main/libe/
• pcre2 is no longer available here: https://apt-test.freedom.press/pool/main/p/

[conorsch]

We're still seeing the unwanted package in the test repo, so our CD logic for the test servers should be tweaked. At first I suspected we were still seeing the package served https://apt-test.freedom.press/pool/main/libe/libevent1/ but that was only via HTTP, not via apt. Clearly that's not the case, however:

sdadmin@sd-app:~$ apt-cache policy libevent-1.4-2
libevent-1.4-2:
  Installed: (none)
  Candidate: 1.4.14b-stable-0ubuntu1
  Version table:
     1.4.14b-stable-0ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        500 https://apt-test.freedom.press xenial/main amd64 Packages

So, more action required on the back end to clean up. I suspect the additional cleanup steps are only required on apt-test, and prod apt will remove them smoothly, but will comment further after investigation.