Remove unused function prototype
Commit
aafc05de1bf5 removed StartSlotSyncWorker() but mistakenly left
the prototype in slotsync.h. Fix by removing.
Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/
3F577953-A29E-4722-98AD-
2DA9EFF2CBB8@yesql.se