fix(lint): remove unused isBackendIconKnown, unblocking CI

Pre-existing dead code (defined, never imported anywhere) that also
tripped react-refresh/only-export-components since it mixed a
non-component export into a component-only file — eslint treats that
as an error, which was silently failing every CI run's lint step
(including this release build) well before this session's changes.

src/components/common/BackendIcon.tsx

@@ -94,12 +94,6 @@ export function BackendIcon({ backend, className, fallback = null }: BackendIcon
   );
 }
 
-export function isBackendIconKnown(backend: string | null | undefined): boolean {
-  if (!backend) return false;
-  const key = backend.toLowerCase().replace(/[^a-z0-9]/g, '');
-  return Boolean(BACKEND_ICONS[key] ?? BACKEND_ICONS[backend.toLowerCase()]);
-}
-
 interface BackendVariantIconProps {
   variant: { name: string; label: string };
   className?: string;