beam-modules/hex-snapshot: remove

The package set is not maintained. It is also not used by most of the
BEAM community. Removing it to allow a more useful set of tools fit to
the BEAM community in Nixpkgs.

pkgs/development/beam-modules/mix-bootstrap

@@ -25,8 +25,7 @@
 -record(data, {version
               , erl_libs
               , root
-              , name
-              , registry_snapshot}).
+              , name}).
 -define(LOCAL_HEX_REGISTRY, "registry.ets").
 
 main(Args) ->
@@ -51,8 +50,7 @@ gather_required_data_from_the_environment(_) ->
     {ok, #data{ version = guard_env("version")
               , erl_libs = os:getenv("ERL_LIBS", [])
               , root = code:root_dir()
-              , name = guard_env("name")
-              , registry_snapshot = guard_env("HEX_REGISTRY_SNAPSHOT")}}.
+              , name = guard_env("name")}}.
 
 -spec guard_env(string()) -> string().
 guard_env(Name) ->