Drop "unrolled/render" package (#23965)

None of the features of `unrolled/render` package is used. 

The Golang builtin "html/template" just works well. Then we can improve
our HTML render to resolve the "$.root.locale.Tr" problem as much as
possible.

Next step: we can have a template render pool (by Clone), then we can
inject global functions with dynamic context to every `Execute` calls.
Then we can use `{{Locale.Tr ....}}` directly in all templates , no need
to pass the `$.root.locale` again and again.

go.mod

@@ -96,7 +96,6 @@ require (
 	github.com/stretchr/testify v1.8.1
 	github.com/syndtr/goleveldb v1.0.0
 	github.com/tstranex/u2f v1.0.0
-	github.com/unrolled/render v1.5.0
 	github.com/urfave/cli v1.22.12
 	github.com/xanzy/go-gitlab v0.80.2
 	github.com/xeipuuv/gojsonschema v1.2.0