refactor(3p/gerrit-queue): use go:embed, bump go1.16, drop shell.nix

Previously, gerrit-queue used statik to embed files. Since go1.16, we
have go:embed, which solves this much nicer, without any requirements to
have the statik binary around.

As the only other thing the shell.nix and .envrc plumbing did was bring
a version of Go in scope, it's dropped now. We assume to have a
recent-enough go binary around, else go will complain.

Imported from https://github.com/flokli/gerrit-queue/pull/9

Change-Id: I851b06777a29d4f2d955cf3a7db6455a7189bc46
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4329
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Autosubmit: tazjin <mail@tazj.in>

third_party/gerrit-queue/public/serie.tmpl.html

@@ -1,19 +0,0 @@
-{{ define "serie" }}
-<table class="table table-sm table-hover">
-<thead class="thead-light">
-    <tr>
-    <th scope="col">Owner</th>
-    <th scope="col">Changeset</th>
-    <th scope="col">Flags</th>
-    </tr>
-</thead>
-<tbody>
-    <tr>
-        <td colspan="3" class="table-success">Serie with {{ len .ChangeSets }} changes</td>
-    </tr>
-    {{ range $changeset := .ChangeSets }}
-    {{ block "changeset" $changeset }}{{ end }}
-    {{ end }}
-</tbody>
-</table>
-{{ end }}