wallpaper.h: Remove useless _XFUNCPROTO wrappers

feh is C code, _XFUNCPROTO(BEGIN|END) are only needed for C++ applications.

src/wallpaper.h

@@ -42,7 +42,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 extern Window ipc_win;
 extern Atom ipc_atom;
 
-_XFUNCPROTOBEGIN extern Window enl_ipc_get_win(void);
+extern Window enl_ipc_get_win(void);
 extern void enl_ipc_send(char *);
 extern char *enl_wait_for_reply(void);
 extern char *enl_ipc_get(const char *);
@@ -53,5 +53,4 @@ extern int feh_wm_get_num_desks(void);
 extern signed char feh_wm_get_wm_is_e(void);
 void feh_wm_set_bg_filelist(unsigned char bgmode);
 
-_XFUNCPROTOEND
 #endif