Remove shift+backspace -> ^H binding

This has been there since the first commit of term.js, it's not clear
why it's there but Terminal.app, iTerm2 and kitty seem to just do a
regular backspace

Fixes #3759

src/common/input/Keyboard.ts

@@ -83,10 +83,7 @@ export function evaluateKeyboardEvent(
       break;
     case 8:
       // backspace
-      if (ev.shiftKey) {
-        result.key = C0.BS; // ^H
-        break;
-      } else if (ev.altKey) {
+      if (ev.altKey) {
         result.key = C0.ESC + C0.DEL; // \e ^?
         break;
       }