USER_LOCK is not a default package of SYS, you need to install it before using it.
SQL> conn / as sysdba
drop package user_lock
ERROR at line 1:
ORA-04043: object USER_LOCK does not exist
Warning: Package Body created with compilation errors.
The error ORA-04043 is very normal for the first time installation, simply because userlock.sql tries to drop USER_LOCK package before creating a new one for you.
Please note that, Synonym created. means that a public synonym for the package with the same name has been created.
The last Grant succeeded. means that the following privilege has been granted successfully.
grant execute on user_lock to public;
Therefore, you don't have to grant it to PUBLIC again.