Fix tests for replication slots stats.

Some of the tests were not considering that the slot's spill stats could be
received by the stats collector after we have reset the stats. Remove
those tests and don't check total bytes decoded and sent to output plugin
in the spilled stats test as we can send the spilled stats to the stats
collector before actually sending the changes to output plugin.

Reported-by: Tom Lane as per buildfarm
Author: Vignesh C, Sawada Masahiko
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/20210319185247.ldebgpdaxsowiflw@alap3.anarazel.de

contrib/test_decoding/expected/stats.out

@@ -111,48 +111,10 @@ SELECT wait_for_decode_stats(false, true);
  
 (1 row)
 
-SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots;
-       slot_name       | spill_txns | spill_count | total_txns | total_bytes 
------------------------+------------+-------------+------------+-------------
- regression_slot_stats | t          | t           | t          | t
-(1 row)
-
--- reset the slot stats, and wait for stats collector to reset
-SELECT pg_stat_reset_replication_slot('regression_slot_stats');
- pg_stat_reset_replication_slot 
---------------------------------
- 
-(1 row)
-
-SELECT wait_for_decode_stats(true, true);
- wait_for_decode_stats 
------------------------
- 
-(1 row)
-
-SELECT slot_name, spill_txns, spill_count, total_txns, total_bytes FROM pg_stat_replication_slots;
-       slot_name       | spill_txns | spill_count | total_txns | total_bytes 
------------------------+------------+-------------+------------+-------------
- regression_slot_stats |          0 |           0 |          0 |           0
-(1 row)
-
--- decode and check stats again.
-SELECT count(*) FROM pg_logical_slot_peek_changes('regression_slot_stats', NULL, NULL, 'skip-empty-xacts', '1');
- count 
--------
-  5002
-(1 row)
-
-SELECT wait_for_decode_stats(false, true);
- wait_for_decode_stats 
------------------------
- 
-(1 row)
-
-SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots;
-       slot_name       | spill_txns | spill_count | total_txns | total_bytes 
------------------------+------------+-------------+------------+-------------
- regression_slot_stats | t          | t           | t          | t
+SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count FROM pg_stat_replication_slots;
+       slot_name       | spill_txns | spill_count 
+-----------------------+------------+-------------
+ regression_slot_stats | t          | t
 (1 row)
 
 -- Ensure stats can be repeatedly accessed using the same stats snapshot. See

contrib/test_decoding/sql/stats.sql

@@ -73,17 +73,7 @@ SELECT count(*) FROM pg_logical_slot_peek_changes('regression_slot_stats', NULL,
 -- exact stats count as that can vary if any background transaction (say by
 -- autovacuum) happens in parallel to the main transaction.
 SELECT wait_for_decode_stats(false, true);
-SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots;
-
--- reset the slot stats, and wait for stats collector to reset
-SELECT pg_stat_reset_replication_slot('regression_slot_stats');
-SELECT wait_for_decode_stats(true, true);
-SELECT slot_name, spill_txns, spill_count, total_txns, total_bytes FROM pg_stat_replication_slots;
-
--- decode and check stats again.
-SELECT count(*) FROM pg_logical_slot_peek_changes('regression_slot_stats', NULL, NULL, 'skip-empty-xacts', '1');
-SELECT wait_for_decode_stats(false, true);
-SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots;
+SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count FROM pg_stat_replication_slots;
 
 -- Ensure stats can be repeatedly accessed using the same stats snapshot. See
 -- https://postgr.es/m/20210317230447.c7uc4g3vbs4wi32i%40alap3.anarazel.de