pgsql: Revert addition of pg_terminate_backend() because of race

Log Message:
-----------
Revert addition of pg_terminate_backend() because of race conditions.

Modified Files:
--------------
    pgsql/doc:
        TODO (r1.2420 -> r1.2421)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/TODO?r1=1.2420&r2=1.2421)
    pgsql/doc/src/FAQ:
        TODO.html (r1.926 -> r1.927)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html?r1=1.926&r2=1.927)
    pgsql/doc/src/sgml:
        func.sgml (r1.431 -> r1.432)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.431&r2=1.432)
        runtime.sgml (r1.412 -> r1.413)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/runtime.sgml?r1=1.412&r2=1.413)
    pgsql/src/backend/tcop:
        postgres.c (r1.549 -> r1.550)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c?r1=1.549&r2=1.550)
    pgsql/src/backend/utils/adt:
        misc.c (r1.60 -> r1.61)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/misc.c?r1=1.60&r2=1.61)
    pgsql/src/include/catalog:
        pg_proc.h (r1.490 -> r1.491)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.490&r2=1.491)
    pgsql/src/include/storage:
        proc.h (r1.105 -> r1.106)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/proc.h?r1=1.105&r2=1.106)
    pgsql/src/include/utils:
        builtins.h (r1.313 -> r1.314)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h?r1=1.313&r2=1.314)