offlineimap: update to 8.0.0; remove dispensable py2 deps

[icp1994]

Testing the changes

• I tested the changes in this PR: NO

Local build testing

• I built this PR locally for my native architecture, x86_64

This update migrates the package to python 3. Two of the python 2 dependencies under the old full-deptree don't have any more dependent packages. I removed one of them outright. For the other, which provided a python 3 counterpart as subpackage, removed the python 2 package and converted the python 3 symlinked package to be its own module.

I DID NOT do any significant runtime testing on the updated offlineimap package expect for installing and running --version, --help etc.

[leahneukirchen]

Do not merge without my approval please.

[leahneukirchen]

GitHub Actions doesn't do IPv6, please disable these tests too.

[icp1994]

Maybe I got the commit order wrong? Seemed okay to me but some builds are confused about not finding the imaplib2 lib while others work fine :/

[leahneukirchen]

python3-imaplib2 needs to be in hostmakedepends too if it's needed during build

[icp1994]

Ah, everything under $depends of offlineimap were needed for building too. But I never noticed anything locally since they were always getting pulled in for checkdepends. That's my guess since every CI with test passed the build.

[leahneukirchen]

Used it for three days, seems to work fine and even is a bit faster.

[classabbyamp]

@leahneukirchen still working well? can this be merged?