chore: drop Dockerfile comment

Dockerfile

@@ -5,9 +5,6 @@ WORKDIR /build/mta-sign-ui
 
 COPY mta-sign-ui/package.json mta-sign-ui/pnpm-lock.yaml* ./
 
-# Pin pnpm to the version declared in mta-sign-ui/package.json ("packageManager");
-# an unpinned global install drifts to new majors (pnpm 12 hard-errors on
-# unapproved build scripts).
 RUN npm install -g pnpm@10.33.0
 
 COPY mta-sign-ui/ ./