[gegl] Fix build with glib 2.67.3 (see https://gitlab.gnome.org/GNOME/glib/-/issues/2331).

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 130cd583530dc41adfdec76d6662302f833e6033
Author: Olivier Tilloy <olivier tilloy canonical com>
Date:   Fri Mar 5 12:58:18 2021 +0100

    Fix build with glib 2.67.3 (see https://gitlab.gnome.org/GNOME/glib/-/issues/2331).

 operations/external/exr-load.cpp | 2 --
 1 file changed, 2 deletions(-)
---
diff --git a/operations/external/exr-load.cpp b/operations/external/exr-load.cpp
index e864f7e3e..28403639c 100644
--- a/operations/external/exr-load.cpp
+++ b/operations/external/exr-load.cpp
@@ -29,9 +29,7 @@ property_file_path (path, "File", "")
 #define GEGL_OP_NAME exr_load
 #define GEGL_OP_C_FILE       "exr-load.cpp"
 
-extern "C" {
 #include "gegl-op.h"
-}
 
 #include <ImfInputFile.h>
 #include <ImfChannelList.h>