remove arclink client

[megies]

What does this PR do?

Removes arclink client

Why was it initiated? Any relevant Issues?

It has been deprecated for years, officially discontinued and main
servers have been shut down years ago. no point dragging this along

PR Checklist

• Correct base branch selected? master for new features, maintenance_... for bug fixes
• This PR is not directly related to an existing issue (which has no PR yet).
• If the PR is making changes to documentation, docs pages can be built automatically.
  Just add the "build_docs" tag to this PR.
• If all tests including network modules (e.g. clients.fdsn) should be tested for the PR,
  just add the "test_network" tag to this PR.
• All tests still pass.
• Any new features or fixed regressions are covered via new tests.
• Any new or changed features are fully documented.
• Significant changes have been added to CHANGELOG.txt .
• First time contributors have added your name to CONTRIBUTORS.txt .
• If the changes affect any plotting functions you have checked that the plots
  from all the CI builds look correct. Add the "upload_plots" tag so that plotting
  outputs are attached as artifacts.
• Add the "ready for review" tag when you are ready for the PR to be reviewed.

@trichter, feel free to bump to a later release

[trichter]

For me it's both OK, remove it now or right after the release of 1.3.0.

[d-chambers]

Should we think about removing the other depreciated modules at the same time?

[megies]

Should we think about removing the other depreciated modules at the same time?

which ones? but probably.. yes.. since its been a real long time since last release anyway

[d-chambers]

which ones? but probably.. yes.. since its been a real long time since last release anyway

At least obspy.db and obspy.client.sieshub

[megies]

At least obspy.db and obspy.client.sieshub

I'd say yes, let's get rid of those two as well this release. I don't think these see much use anymore and we still have them in previous releases.

[megies]

Hmm.. actually, I realized that they have not been marked deprecated in last release, only in master. So.. not sure

[megies]

I'll push the remove commit anyway, since I was already done. Can still discuss and roll back that commit here

[d-chambers]

I don't think it is a big deal since they probably aren't used much anyway, but I don't have a strong opinion.

[trichter]

It's also no big deal if they stay in the next release. Both options are good with me.

[megies]

I got rid of the second commit (ff6a217) that removed db and clients.seishub, to stay in line with our policy of showing a deprecation message for at least one major release before removing stuff.

[megies]

Rebased on current master

[megies]

Good to go from my point of view

[trichter]

Sorry, another line in pytest.ini can be removed.

[trichter]

I got rid of the second commit (ff6a217) that removed db and clients.seishub, to stay in line with our policy of showing a deprecation message for at least one major release before removing stuff.

You could move it to another branch. We can merge it after the release.