bindings: recognize ASCII DEL as backspace also in viewer and browser

This completes the fix for https://savannah.gnu.org/bugs/?54978.
Reported-by: David Lawrence Ramsey <pooka109@gmail.com>

src/browser.c

@@ -465,6 +465,7 @@ functionptrtype parse_browser_input(int *kbinput)
 			case ' ':
 				return do_page_down;
 			case '-':
+			case DEL_CODE:
 				return do_page_up;
 			case '?':
 				return do_help_void;

src/help.c

@@ -570,6 +570,7 @@ functionptrtype parse_help_input(int *kbinput)
 			case ' ':
 				return do_page_down;
 			case '-':
+			case DEL_CODE:
 				return do_page_up;
 			case 'W':
 			case 'w':