fix(diff): prune empty channel when old model is empty

[jpower432]

Description of the change:

In this PR, the opm alpha diff command will now prune empty channels when an include config is provided in headsOnly mode.

Motivation for the change:
The motivation for this change to allow the catalog index produced in this instance to pass opm validate and be usable with a cluster.

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Docs updated or added to /docs
• Commit messages sensible and descriptive

Closes #883

[openshift-ci]

Hi @jpower432. Thanks for your PR.

I'm waiting for a operator-framework member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[estroz]

/ok-to-test

[estroz]

If this is only called once, in-line the code in that spot. Perhaps this could live in Includer.Run() too.

[jpower432]

Moved this down to where I was calling it. The only reason I didn't put it in Includer.Run() is because this is only an issue when IncludeAdditively is false I believe.

[codecov]

Codecov Report

Merging #884 (fb65ae2) into master (808de07) will decrease coverage by 0.00%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #884      +/-   ##
==========================================
- Coverage   52.06%   52.06%   -0.01%     
==========================================
  Files         103      103              
  Lines        9069     9072       +3     
==========================================
+ Hits         4722     4723       +1     
- Misses       3440     3441       +1     
- Partials      907      908       +1     

Impacted Files	Coverage Δ
alpha/declcfg/diff.go	76.92% <33.33%> (-0.57%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 808de07...fb65ae2. Read the comment docs.

[estroz]

/approve
/lgtm

[dinhxuanvu]

Looks good.

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dinhxuanvu, estroz, jpower432

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [dinhxuanvu]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment