Remove pg_audit

This removes pg_audit, per discussion:

20150528082038.GU26667@tamriel.snowman.net

contrib/pg_audit/.gitignore

-log/
-results/
-tmp_check/
-regression.diffs
-regression.out

contrib/pg_audit/Makefile

-# contrib/pg_audit/Makefile
-
-MODULE_big = pg_audit
-OBJS = pg_audit.o $(WIN32RES)
-
-EXTENSION = pg_audit
-DATA = pg_audit--1.0.sql
-PGFILEDESC = "pg_audit - An audit logging extension for PostgreSQL"
-
-REGRESS = pg_audit
-
-ifdef USE_PGXS
-PG_CONFIG = pg_config
-PGXS := $(shell $(PG_CONFIG) --pgxs)
-include $(PGXS)
-else
-subdir = contrib/pg_audit
-top_builddir = ../..
-include $(top_builddir)/src/Makefile.global
-include $(top_srcdir)/contrib/contrib-global.mk
-endif

contrib/pg_audit/pg_audit--1.0.sql

-/* pg_audit/pg_audit--1.0.sql */
-
--- complain if script is sourced in psql, rather than via CREATE EXTENSION
-\echo Use "CREATE EXTENSION pg_audit" to load this file.\quit
-
-CREATE FUNCTION pg_audit_ddl_command_end()
-	RETURNS event_trigger
-	LANGUAGE C
-	AS 'MODULE_PATHNAME', 'pg_audit_ddl_command_end';
-
-CREATE EVENT TRIGGER pg_audit_ddl_command_end
-	ON ddl_command_end
-	EXECUTE PROCEDURE pg_audit_ddl_command_end();
-
-CREATE FUNCTION pg_audit_sql_drop()
-	RETURNS event_trigger
-	LANGUAGE C
-	AS 'MODULE_PATHNAME', 'pg_audit_sql_drop';
-
-CREATE EVENT TRIGGER pg_audit_sql_drop
-	ON sql_drop
-	EXECUTE PROCEDURE pg_audit_sql_drop();

contrib/pg_audit/pg_audit.control

-# pg_audit extension
-comment = 'provides auditing functionality'
-default_version = '1.0'
-module_pathname = '$libdir/pg_audit'
-relocatable = true