revert(ds): Don't duplicate the clean start in session_ds

apps/emqx/src/emqx_persistent_session_ds.erl

@@ -153,8 +153,6 @@ open(#{clientid := ClientID} = _ClientInfo, ConnInfo) ->
     %% somehow isolate those idling not-yet-expired sessions into a separate process
     %% space, and move this call back into `emqx_cm` where it belongs.
     ok = emqx_cm:discard_session(ClientID),
-    case maps:get(clean_start, ConnInfo, false) of
-        false ->
     case session_open(ClientID, ConnInfo) of
         Session0 = #{} ->
             ensure_timers(),
@@ -163,10 +161,6 @@ open(#{clientid := ClientID} = _ClientInfo, ConnInfo) ->
             {true, Session, []};
         false ->
             false
-            end;
-        true ->
-            session_drop(ClientID),
-            false
     end.
 
 ensure_session(ClientID, ConnInfo, Conf) ->
@@ -554,7 +548,7 @@ session_open(SessionId, NewConnInfo) ->
                 EI = expiry_interval(ConnInfo),
                 case ?IS_EXPIRED(NowMS, DisconnectedAt, EI) of
                     true ->
-                        %% Should we drop the session now, or leave it to session GC?
+                        session_drop(SessionId),
                         false;
                     false ->
                         %% new connection being established
@@ -831,8 +825,13 @@ session_drop_pubranges(DSSessionId) ->
 %%--------------------------------------------------------------------------------
 
 transaction(Fun) ->
+    case mnesia:is_transaction() of
+        true ->
+            Fun();
+        false ->
             {atomic, Res} = mria:transaction(?DS_MRIA_SHARD, Fun),
-    Res.
+            Res
+    end.
 
 ro_transaction(Fun) ->
     {atomic, Res} = mria:ro_transaction(?DS_MRIA_SHARD, Fun),