chore: remove CDK_ASSETS version flag

[mrgrain]

Not needed anymore. No change to synth'd files.

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.13%. Comparing base (2093af0) to head (4e8dd97).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #434      +/-   ##
==========================================
+ Coverage   79.86%   80.13%   +0.26%     
==========================================
  Files          65       65              
  Lines        6900     6900              
  Branches      787      793       +6     
==========================================
+ Hits         5511     5529      +18     
+ Misses       1366     1349      -17     
+ Partials       23       22       -1     

Flag	Coverage Δ
suite.unit	80.13% <ø> (+0.26%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.