removed useless dotnet build

backend/Dockerfile

@@ -9,7 +9,6 @@ ENV BUILD_CONFIG Release
 
 RUN cd /tmp/backend && \
     dotnet restore && \
-    find . -name project.json | xargs dotnet build -c ${BUILD_CONFIG} && \
     mkdir /var/www && \
     cd /tmp/backend/${WEBAPI_PROJECT} && \
     dotnet publish --output /var/www && \