test(emqx): remove `peercert` from clientinfo fixtures

According to typespec, there's no place for `peercert` in
`clientinfo()`.

apps/emqx/test/emqx_access_control_SUITE.erl

@@ -116,7 +116,6 @@ clientinfo(InitProps) ->
             username => <<"username">>,
             password => <<"passwd">>,
             is_superuser => false,
-            peercert => undefined,
             mountpoint => undefined
         },
         InitProps

apps/emqx/test/emqx_channel_SUITE.erl

@@ -1211,7 +1211,6 @@ clientinfo(InitProps) ->
             clientid => <<"clientid">>,
             username => <<"username">>,
             is_superuser => false,
-            peercert => undefined,
             mountpoint => undefined
         },
         InitProps

apps/emqx/test/emqx_connection_SUITE.erl

@@ -676,7 +676,6 @@ channel(InitFields) ->
         clientid => <<"clientid">>,
         username => <<"username">>,
         is_superuser => false,
-        peercert => undefined,
         mountpoint => undefined
     },
     Conf = emqx_cm:get_session_confs(ClientInfo, #{

apps/emqx/test/emqx_ws_connection_SUITE.erl

@@ -33,17 +33,6 @@
     ]
 ).
 
--define(STATS_KEYS, [
-    recv_oct,
-    recv_cnt,
-    send_oct,
-    send_cnt,
-    recv_pkt,
-    recv_msg,
-    send_pkt,
-    send_msg
-]).
-
 -define(ws_conn, emqx_ws_connection).
 
 all() -> emqx_common_test_helpers:all(?MODULE).
@@ -618,7 +607,6 @@ channel(InitFields) ->
         clientid => <<"clientid">>,
         username => <<"username">>,
         is_superuser => false,
-        peercert => undefined,
         mountpoint => undefined
     },
     Conf = emqx_cm:get_session_confs(ClientInfo, #{