fix(schema): do not validate etc_dir

apps/emqx_machine/src/emqx_machine_schema.erl

@@ -309,24 +309,8 @@ fields("node") ->
          )}
     , {"etc_dir",
        sc(string(),
-          #{
-             converter => fun(EtcDir) ->
-                case filename:absname(EtcDir) =:= EtcDir of
-                   true -> 
-                      unicode:characters_to_list(EtcDir);
-                   false ->
-                      unicode:characters_to_list(filename:join([code:lib_dir(), "..", EtcDir]))
-                end
-              end,
-             validator => fun(Path) ->
-                case filelib:is_dir(Path) of
-                   true -> 
-                      ok;
-                   false -> 
-                      error({not_dir, Path})
-                end
-               end
-            }
+          #{ desc => "`etc` dir for the node"
+           }
          )}
     ];