docs: remove v1 docs (#4943)

We no longer allow running v1 config, and users can look at old
docs if they want to see the v1 docs still.

Also fix a doc issue in the /server_info admin endpoint.

Signed-off-by: Matt Klein <mklein@lyft.com>

Mirrored from https://github.com/envoyproxy/envoy @ 8aba108eda816ea29dc80b973a1387257cd209c6

docs/BUILD

@@ -16,6 +16,7 @@ proto_library(
         "//envoy/admin/v2alpha:clusters",
         "//envoy/admin/v2alpha:config_dump",
         "//envoy/admin/v2alpha:memory",
+        "//envoy/admin/v2alpha:server_info",
         "//envoy/api/v2:cds",
         "//envoy/api/v2:discovery",
         "//envoy/api/v2:eds",