refactor(sidebar): drop orphaned sidebar-collapse-btn class

Its CSS rule was removed with the data-sidebar-collapsed mask; the button's
collapse behavior is fully driven by the React isCollapsed ternary, leaving the
class name pointing at nothing.

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/w/components/sidebar/sidebar.tsx

@@ -1297,7 +1297,7 @@ export const Sidebar = memo(function Sidebar({ initialCollapsed = false }: Sideb
                   type='button'
                   onClick={toggleCollapsed}
                   className={cn(
-                    'sidebar-collapse-btn ml-2 flex h-[30px] items-center justify-center overflow-hidden rounded-lg transition-all duration-200 hover-hover:bg-[var(--surface-active)]',
+                    'ml-2 flex h-[30px] items-center justify-center overflow-hidden rounded-lg transition-all duration-200 hover-hover:bg-[var(--surface-active)]',
                     isCollapsed ? 'w-0 opacity-0' : 'w-[30px] opacity-100'
                   )}
                   aria-label='Collapse sidebar'