pgsql: Remove pg_plan_queries()'s now-useless needSnapshot parameter.

Log Message:
-----------
Remove pg_plan_queries()'s now-useless needSnapshot parameter. It's useless
in 8.3, too, but I'm not back-patching this change since it would break any
extension modules that might be calling that function.

Modified Files:
--------------
pgsql/src/backend/commands:
prepare.c (r1.92 -> r1.93)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/prepare.c?r1=1.92&r2=1.93)
pgsql/src/backend/executor:
spi.c (r1.201 -> r1.202)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/spi.c?r1=1.201&r2=1.202)
pgsql/src/backend/tcop:
postgres.c (r1.561 -> r1.562)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c?r1=1.561&r2=1.562)
pgsql/src/backend/utils/cache:
plancache.c (r1.24 -> r1.25)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/plancache.c?r1=1.24&r2=1.25)
pgsql/src/include/tcop:
tcopprot.h (r1.95 -> r1.96)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/tcop/tcopprot.h?r1=1.95&r2=1.96)