[MINOR] Code Cleanup / Refactoring

[jaceklaskowski]

trafficstars

Code Cleanup / Refactoring:

• Use vals (not vars)
• Fix scaladocs
• Use constants
• Check table availability with txn.deltaLog.tableExists (not txn.readVersion > -1)
• Import reorg
• Remove unused values

How was this patch tested?

1. ./build/sbt clean package test:compile
2. ./build/sbt clean '++ 2.13.5 ; package ; test:compile'

Waiting for the repo build to execute the entire testsuite.

Does this PR introduce any user-facing changes?

No

[jaceklaskowski]

@scottsand-db Please review 🙏

[jaceklaskowski]

Hey @scottsand-db, can I have your attention to this PR, please? Let me know if there's anything to make things easier and have it merged.