pgsql: Remove inappropriate memory context switch in

Log Message:
-----------
Remove inappropriate memory context switch in shutdown_MultiFuncCall().
This was a thinko introduced in a patch from last February; it results
in memory leakage if an SRF is shut down before the actual end of query,
because subsequent code will be running in a longer-lived context than
it's expecting to be.

Modified Files:
--------------
    pgsql/src/backend/utils/fmgr:
        funcapi.c (r1.42 -> r1.43)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/fmgr/funcapi.c?r1=1.42&r2=1.43)