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.

src/backend/utils/fmgr/funcapi.c

@@ -7,7 +7,7 @@
  * Copyright (c) 2002-2008, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/fmgr/funcapi.c,v 1.42 2008/08/25 22:42:34 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/fmgr/funcapi.c,v 1.43 2008/11/30 18:49:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -182,7 +182,6 @@ shutdown_MultiFuncCall(Datum arg)
 	 * Delete context that holds all multi-call data, including the
 	 * FuncCallContext itself
 	 */
-	MemoryContextSwitchTo(flinfo->fn_mcxt);
 	MemoryContextDelete(funcctx->multi_call_memory_ctx);
 }