[SDK-2487] Reverted minimum sdk version change

[nsingh-branch]

Reference

SDK-SDK -- Reverted minimum sdk version change

Description

Changed the minimum SDK from 23 back to 21 since some clients may not want to upgrade this value in their app yet.

Original PR: #1213

Testing Instructions

Ensure the SDK still builds and integrates properly and all of the SDK's features still function.

Risk Assessment [LOW]

• I, the PR creator, have tested — integration, unit, or otherwise — this code.

Reviewer Checklist (To be checked off by the reviewer only)

• JIRA Ticket is referenced in PR title.
• Correctness & Style
  • Conforms to AOSP Style Guides
  • Mission critical pieces are documented in code and out of code as needed.
• Unit Tests reviewed and test issue sufficiently.
• Functionality was reviewed in QA independently by another engineer on the team.

cc @BranchMetrics/saas-sdk-devs for visibility.

[gdeluna-branch]

Does that PR need to be reverted? Does the tool work with this sdk ver?

[nsingh-branch]

Does that PR need to be reverted? Does the tool work with this sdk ver?

@gdeluna-branch I just tested out Nix and it appears to still be working fine, so the version bump may not be necessary. I've also reached out to allen for confirmation too though.