Revert support for improved tracking of nested queries

This commit reverts the two following commits:
- 499edb0974, track more precisely query locations for nested
statements.
- 06450c7b8c, a follow-up fix of 499edb0974 with query locations.
The test introduced in this commit is not reverted.  This is proving
useful to track a problem that only pgaudit was able to detect.

These prove to have issues with the tracking of SELECT statements, when
these use multiple parenthesis which is something supported by the
grammar.  Incorrect location and lengths are causing pg_stat_statements
to become confused, failing its job in query normalization with
potential out-of-bound writes because the location and the length may
not match with what can be handled.  A lot of the query patterns
discussed when this issue was reported have no test coverage in the main
regression test suite, or the recovery test 027_stream_regress.pl would
have caught the problems as pg_stat_statements is loaded by the node
running the regression tests.  A first step would be to improve the test
coverage to stress more the query normalization logic.

A different portion of this work was done in 45e0ba30fc, with the
addition of tests for nested queries.  These can be left in the tree.
They are useful to track the way inner queries are currently tracked by
PGSS with non-top-level entries, and will be useful when reconsidering
in the future the work reverted here.

Reported-by: Alexander Kozhemyakin <a.kozhemyakin@postgrespro.ru>
Discussion: https://postgr.es/m/18947-cdd2668beffe02bf@postgresql.org

contrib/pg_stat_statements/sql/planning.sql

@@ -20,11 +20,11 @@ SELECT 42;
 SELECT 42;
 SELECT 42;
 SELECT plans, calls, rows, query FROM pg_stat_statements
-  WHERE query NOT LIKE 'SELECT COUNT%' ORDER BY query COLLATE "C";
+  WHERE query NOT LIKE 'PREPARE%' ORDER BY query COLLATE "C";
 -- for the prepared statement we expect at least one replan, but cache
 -- invalidations could force more
 SELECT plans >= 2 AND plans <= calls AS plans_ok, calls, rows, query FROM pg_stat_statements
-  WHERE query LIKE 'SELECT COUNT%' ORDER BY query COLLATE "C";
+  WHERE query LIKE 'PREPARE%' ORDER BY query COLLATE "C";
 
 -- Cleanup
 DROP TABLE stats_plan_test;