pgsql: Remove contrib version of rtree_gist --- now in core system.

Log Message:
-----------
Remove contrib version of rtree_gist --- now in core system.

Modified Files:
--------------
    pgsql/contrib:
        Makefile (r1.56 -> r1.57)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/Makefile.diff?r1=1.56&r2=1.57)
        README (r1.78 -> r1.79)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/README.diff?r1=1.78&r2=1.79)

Removed Files:
-------------
    pgsql/contrib/rtree_gist:
        Makefile
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/Makefile)
        README.rtree_gist
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/README.rtree_gist)
        rtree_gist.c
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/rtree_gist.c)
        rtree_gist.sql.in
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/rtree_gist.sql.in)
    pgsql/contrib/rtree_gist/bench:
        bench.pl
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/bench/bench.pl)
        create_test.pl
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/bench/create_test.pl)
    pgsql/contrib/rtree_gist/data:
        test_box.data
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/data/test_box.data)
    pgsql/contrib/rtree_gist/expected:
        rtree_gist.out
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/expected/rtree_gist.out)
    pgsql/contrib/rtree_gist/sql:
        rtree_gist.sql
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/sql/rtree_gist.sql)