feat(ingest): cleanup deprecated datahub.integrations.airflow.* imports

[hsheth2]

It's been ~6 months or so since these were deprecated, so we should be pretty safe to remove them now.

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable)

[github-actions]

Unit Test Results

     45 files  ±0       45 suites  ±0   40m 39s ⏱️ - 1m 22s
   634 tests ±0     576 ✔️ ±0  58 💤 ±0  0 ❌ ±0 
1 416 runs  ±0  1 336 ✔️ ±0  80 💤 ±0  0 ❌ ±0 

Results for commit 636e896. ± Comparison against base commit a6deaab.

[shirshanka]

LGTM