Remove redundant Auspice build

Auspice has a prepare script that runs the build script automatically
after npm install. This means the explicit call to run the build script
is redundant and can be removed to improve build times.

Dockerfile

@@ -203,7 +203,6 @@ RUN /builder-scripts/download-repo https://github.com/nextstrain/auspice release
     --arch=$TARGETARCH \
  && npm install \
     --arch=$TARGETARCH \
- && npm run build \
  && npm link
 
 # ———————————————————————————————————————————————————————————————————— #