remove deprecated v2alpha1 flag

[celenechang]

What does this PR do?

Remove deprecated flag.

In a subsequent PR, references to V2Enabled will be removed.

Motivation

What inspired you to submit this pull request?

Additional Notes

Anything else we should know when reviewing?

Minimum Agent Versions

Are there minimum versions of the Datadog Agent and/or Cluster Agent required?

• Agent: vX.Y.Z
• Cluster Agent: vX.Y.Z

Describe your test plan

Ensure v2alpha1 DatadogAgent CR reconciles as expected.

Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.54%. Comparing base (ef9a40c) to head (1cf2d4c).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1189   +/-   ##
=======================================
  Coverage   59.54%   59.54%           
=======================================
  Files         174      174           
  Lines       21598    21598           
=======================================
  Hits        12861    12861           
  Misses       7958     7958           
  Partials      779      779           

Flag	Coverage Δ
unittests	59.54% <ø> (ø)

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