PG-320: Removal of state columnns from pgsm view.

We are concerned with finished queries in pg_stat_monitor, so state and
state_code columns were removed from the pg_stat_monitor_view as we only
list finished queries on it.

Removed state regression as it is not necessary anymore.

Also, this allowed us to remove the call to pgss_store on ExecutorStart,
which just updated query state to EXEC, thus saving some CPU.

regression/sql/state.sql

@@ -1,8 +0,0 @@
-CREATE EXTENSION pg_stat_monitor;
-SELECT pg_stat_monitor_reset();
-SELECT 1;
-SELECT 1/0;   -- divide by zero
-
-SELECT query, state_code, state FROM pg_stat_monitor ORDER BY query COLLATE "C";
-SELECT pg_stat_monitor_reset();
-DROP EXTENSION pg_stat_monitor;