pg_stat_statements: Remove duplicated tests for SET statements

This looks like a copy-paste mistake introduced in de2aca2885, that
has added checks for more patterns of SET statements while ignoring the
original test block that existed.

Backpatch down to where this has been introduced, as this shaves some
cycles.

Author: Sergei Kornilov
Discussion: https://postgr.es/m/5689421699428803@mail-sendbernar-production-main-46.myt.yp-c.yandex.net
Backpatch-through: 16

contrib/pg_stat_statements/expected/utility.out

@@ -664,30 +664,3 @@ SELECT pg_stat_statements_reset();
  
 (1 row)
 
--- SET statements.
--- These use two different strings, still they count as one entry.
-SET work_mem = '1MB';
-Set work_mem = '1MB';
-SET work_mem = '2MB';
-RESET work_mem;
-SET enable_seqscan = off;
-SET enable_seqscan = on;
-RESET enable_seqscan;
-SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
- calls | rows |               query               
--------+------+-----------------------------------
-     1 |    0 | RESET enable_seqscan
-     1 |    0 | RESET work_mem
-     1 |    1 | SELECT pg_stat_statements_reset()
-     1 |    0 | SET enable_seqscan = off
-     1 |    0 | SET enable_seqscan = on
-     2 |    0 | SET work_mem = '1MB'
-     1 |    0 | SET work_mem = '2MB'
-(7 rows)
-
-SELECT pg_stat_statements_reset();
- pg_stat_statements_reset 
---------------------------
- 
-(1 row)
-

contrib/pg_stat_statements/sql/utility.sql

@@ -329,16 +329,3 @@ DROP TABLE pgss_ctas;
 DROP TABLE pgss_select_into;
 
 SELECT pg_stat_statements_reset();
-
--- SET statements.
--- These use two different strings, still they count as one entry.
-SET work_mem = '1MB';
-Set work_mem = '1MB';
-SET work_mem = '2MB';
-RESET work_mem;
-SET enable_seqscan = off;
-SET enable_seqscan = on;
-RESET enable_seqscan;
-
-SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
-SELECT pg_stat_statements_reset();