PG-174: Code cleanup.

pg_stat_monitor is a bit longer; therefore, it requires some code cleanup.
Therefore I decided to turn these tasks into multiple commits and PR to avoid
various changes in one PR. This will ease the review and Q/A process.
In this commit, I have done these tasks.

 1 - Delete all the SQL.in files because these version-dependent files
 are becoming significant in quantity. Now added a single SQL file for which
 contains the dynamic SQL based on the PostgreSQL Version.

 2 - New SQL files (pg_stat_monitor--2.0.sql) added for pg_stat_monitor version 2.

 3 - A new SQL file (pg_stat_monitor--1.0--2.0.sql) is created, which will be
 used to upgrade from version 1.0 to 2.0. Currently, this file is empty. But
 whenever we add some API changes into 2.0, we need to update that file too.

 4 - The control file (pg_stat_monitor.control) is updated for version 2.0.
 This change will make the CREATE EXTENSION default to pg_stat_monitor version 2.0

Makefile

@@ -4,7 +4,7 @@ MODULE_big = pg_stat_monitor
 OBJS = hash_query.o guc.o pg_stat_monitor.o $(WIN32RES)
 
 EXTENSION = pg_stat_monitor
-DATA = pg_stat_monitor--1.0.sql
+DATA = pg_stat_monitor--1.0.sql pg_stat_monitor--2.0.sql pg_stat_monitor--1.0--2.0.sql
 
 PGFILEDESC = "pg_stat_monitor - execution statistics of SQL statements"
 
@@ -19,7 +19,6 @@ REGRESS = basic version guc counters relations database error_insert application
 # NO_INSTALLCHECK = 1
 
 PG_CONFIG = pg_config
-PGSM_INPUT_SQL_VERSION := 1.0
 
 ifdef USE_PGXS
 MAJORVERSION := $(shell pg_config --version | awk {'print $$2'} | cut -f1 -d".")
@@ -31,20 +30,3 @@ top_builddir = ../..
 include $(top_builddir)/src/Makefile.global
 include $(top_srcdir)/contrib/contrib-global.mk
 endif
-
-ifeq ($(shell test $(MAJORVERSION) -gt 12; echo $$?),0)
-PGSM_INPUT_SQL_VERSION := ${PGSM_INPUT_SQL_VERSION}.${MAJORVERSION}
-endif
-
-$(info Using pg_stat_monitor--${PGSM_INPUT_SQL_VERSION}.sql.in file to generate sql filea.)
-
-ifneq (,$(wildcard ../pg_stat_monitor--${PGSM_INPUT_SQL_VERSION}.sql.in))
-  CP := $(shell cp -v ../pg_stat_monitor--${PGSM_INPUT_SQL_VERSION}.sql.in ../pg_stat_monitor--1.0.sql)
-endif
-ifneq (,$(wildcard pg_stat_monitor--${PGSM_INPUT_SQL_VERSION}.sql.in))
-  CP := $(shell cp -v pg_stat_monitor--${PGSM_INPUT_SQL_VERSION}.sql.in pg_stat_monitor--1.0.sql)
-endif
-
-clean:
-	rm -rf ${DATA}
-	rm -rf t/results

pg_stat_monitor--1.0--2.0.sql

@@ -0,0 +1,5 @@
+/* contrib/pg_stat_monitor/pg_stat_monitor--1.0--2.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "ALTER EXTENSION pg_stat_monitor" to load this file. \quit
+