Drop the env-routing comment

Explained a general Actions practice at a spot where the value is a URL
from our own action, and the pattern is already visible from the env
block two lines below.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019LoLgW7oFjBPxGea9kiZJ2

Author: pattonwebz

.github/workflows/build-plugin-with-ref.yml

@@ -281,8 +281,6 @@ jobs:
         if: github.event_name == 'pull_request'
         uses: actions/github-script@v7
         env:
-          # Routed through env: rather than interpolated into the script body - a
-          # ${{ }} substitution lands in the JS source text before Node parses it.
           PRIMARY_PLAYGROUND_URL: ${{ steps.playground_primary.outputs.playground-url }}
         with:
           script: |