PG 10 streaming replication pg_wal question

Hi LIst,
I am testing PG10 streaming replication ,  with archiving off, I have 
pg_wal on separate directory  to monitor the growth , I had the slave 
offline yesterday  for  more than 20h while I was restoring one of db 
(60GB) with pg_restore from a backup taken with pg_dump, today I brought 
the slave PG host online and replication catch up  nicely , master and 
slave are in sync now, but  on master host the pg_wal is still same  
large size ( as yesterday)  even after all the wal files had been 
applied to salve, would replication process not suppose to removed the 
wal files  on master after being applied to salve ?
( do I need to manually implement a cleanup job of this wal files, as 
mentioned archiving is off on  both servers)
see bellow:

master:  pg_current_wal_lsn
-------------------- C5/D82DDD68

and slave:  pg_last_wal_receive_lsn
------------------------- C5/D82DDD68


and master :
4.0K    ./wal/archive_status
166G    ./wal
last wal file  :
w------- 1 postgres postgres 16777216 Nov 29 16:05 00000007000000C5000000D8

 ans slave :
12K    ./wal/archive_status
1.1G    ./wal

last wal file:
rw------- 1 postgres postgres 16777216 Nov 30 08:56 00000007000000C5000000D8