Remove deprecated `agent.env.agentAutoRegisterEnvironemnts` value

[chadlwilson]

Description

This typoed value was scheduled for removal 3 years ago, but probably forgotten. Should be perfectly safe to remove now.

Checklist

• [x] Chart version bumped in Chart.yaml
• [x] Any new variables have documentation and examples in values.yaml, even if commented out
• [x] Any new variables added to the README.md
• [x] Squash into a single commit (or explain why you'd prefer not to), except...
• [x] ...additional commit added for CHANGELOG.md entry
• [x] Helm lint + tests passing?