Remove 10% safety margin from lock manager hash table estimates

As the comment says, the hash table sizes are just estimates, but that
doesn't mean we need a "safety margin" here. hash_estimate_size()
estimates the needed size in bytes pretty accurately for the given
number of elements, so if we wanted room for more elements in the
table, we should just use larger max_table_size in the
hash_estimate_size() call.

Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Matthias van de Meent <boekewurm+postgres@gmail.com>
Discussion: https://www.postgresql.org/message-id/e07be2ba-856b-4ff5-8313-8b58b6b4e4d0@iki.fi

src/backend/storage/lmgr/lock.c

@@ -3778,11 +3778,6 @@ LockManagerShmemSize(void)
 	max_table_size *= 2;
 	size = add_size(size, hash_estimate_size(max_table_size, sizeof(PROCLOCK)));
 
-	/*
-	 * Since NLOCKENTS is only an estimate, add 10% safety margin.
-	 */
-	size = add_size(size, size / 10);
-
 	return size;
 }