docs: Update keyboard shortcuts to always show "Fn" key option.

Previously, these were only shown for Mac OS users and replaced
the "Home", "End", "PgUp" and "PgDn" shortcuts. But as this really
depends on the keyboard the user is using (there are Mac keyboards
with the above keys), we instead show both options in our web app
and help center documentation on keyboard shortcuts.

The tooltip for the "Scroll to bottom" button will now always show
"End" for all users. Previously, it showed a "Fn" key option for
Mac users.

Fixes #31815.

tools/linter_lib/custom_check.py

@@ -161,12 +161,6 @@ js_rules = RuleList(
                 "web/tests/",
                 "web/src/billing/",
             },
-            "exclude_line": {
-                (
-                    "web/src/common.ts",
-                    '$(this).before($("<kbd>").text("Fn"), $("<span>").text(" + ").contents());',
-                ),
-            },
         },
         {
             "pattern": r"""report.success\(["']""",