Remove exceptions from src/box/func.cc

Mixing C-style error handling and C++ exceptions can lead to
serious problems.

In context of #910

src/box/CMakeLists.txt

@@ -77,7 +77,7 @@ add_library(box STATIC
     vy_log.c
     vy_upsert.c
     space.cc
-    func.cc
+    func.c
     alter.cc
     schema.cc
     session.cc

src/box/func.cc → src/box/func.c

@@ -33,7 +33,6 @@
 #include <dlfcn.h>
 
 #include "lua/utils.h"
-#include "scoped_guard.h"
 
 /**
  * Parsed symbol and package names.

src/box/func.h

@@ -61,9 +61,6 @@ struct func {
 	struct access access[BOX_USER_MAX];
 };
 
-#if defined(__cplusplus)
-} /* extern "C" */
-
 struct func *
 func_new(struct func_def *def);
 
@@ -80,6 +77,9 @@ int
 func_call(struct func *func, box_function_ctx_t *ctx, const char *args,
 	  const char *args_end);
 
+#if defined(__cplusplus)
+} /* extern "C" */
+
 #endif /* defined(__cplusplus) */
 
 #endif /* TARANTOOL_BOX_FUNC_H_INCLUDED */