Obsolete fmgr() declaration in fmgr.h

Hi Hackers,

Commit 5ded4bd21403e143dd3eb66b92d52732fdac1945 removed support for
version-0 function calling convention, and with it the fmgr() function.
However, the declaration was left behind in fmgr.h.  The attached patch
finishes the cleanup.

Regards,

- ilmari
-- 
"I use RMS as a guide in the same way that a boat captain would use
 a lighthouse.  It's good to know where it is, but you generally
 don't want to find yourself in the same spot." - Tollef Fog Heen

From 920a2d39b0f8996801877439d1064a0a7be32b35 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dagfinn=20Ilmari=20Manns=C3=A5ker?= <ilmari@ilmari.org>
Date: Tue, 16 Jan 2018 12:44:26 +0000
Subject: [PATCH] Remove left-over fmgr() declaration

Commit 5ded4bd21403e143dd3eb66b92d52732fdac1945 removed support for
version-0 function calling convention, and with it the fmgr()
function.  However, the declaration was left behind in fmgr.h.
---
 src/include/fmgr.h | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index 665dd76b12..69786bfca8 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -730,19 +730,4 @@ extern PGDLLIMPORT fmgr_hook_type fmgr_hook;
 #define FmgrHookIsNeeded(fn_oid)                            \
     (!needs_fmgr_hook ? false : (*needs_fmgr_hook)(fn_oid))
 
-/*
- * !!! OLD INTERFACE !!!
- *
- * fmgr() is the only remaining vestige of the old-style caller support
- * functions.  It's no longer used anywhere in the Postgres distribution,
- * but we should leave it around for a release or two to ease the transition
- * for user-supplied C functions.  OidFunctionCallN() replaces it for new
- * code.
- */
-
-/*
- * DEPRECATED, DO NOT USE IN NEW CODE
- */
-extern char *fmgr(Oid procedureId,...);
-
 #endif                            /* FMGR_H */
-- 
2.16.1