funcsave: avoid the edited function's path being a temporary file

As functions know where they are loaded from now, there is no point in
them being marked as loaded from a temporary file that has been removed.
Source the function via a redirect instead.

share/functions/funced.fish

@@ -107,7 +107,7 @@ function funced --description 'Edit function definition'
                 end
             end
 
-            if not source $tmpname
+            if not source <$tmpname
                 # Failed to source the function file. Prompt to try again.
                 echo # add a line between the parse error and the prompt
                 set -l repeat