pgsql: Remove inappropriate memory context switch in

Log Message:
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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.

Tags:
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REL8_2_STABLE

Modified Files:
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    pgsql/src/backend/utils/fmgr:
        funcapi.c (r1.31.2.1 -> r1.31.2.2)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/fmgr/funcapi.c?r1=1.31.2.1&r2=1.31.2.2)