move templates from rakyll/statik to go:embed

There is no need for the rakyll/statik package starting with Go 1.16,
which provides us with tools for embedding files
without third-party libraries.

Dockerfile.artifacts

@@ -36,8 +36,6 @@ RUN \
     export WEB_ROOT=/build/backend/web && \
     find . -regex '.*\.\(html\|js\|mjs\)$' -print -exec sed -i "s|{% REMARK_URL %}|http://127.0.0.1:8080|g" {} \; && \
     statik --src=${WEB_ROOT} --dest=/build/backend/app/rest -p api -f && \
-    statik --src=/build/backend/templates --dest=/build/backend/app -p templates -ns templates -f && \
-    ls -la /build/backend/app/templates/statik.go && \
     ls -la /build/backend/app/rest/api/statik.go && \
     ls -la /build/backend/web/