chore: Revert changes made to ui crate structure (#17516)

As a part of https://github.com/zed-industries/zed/pull/17488 I
flattened module structure of ui crate to fix module_inception lint.
However, that's actually unnecessary as we can pass that lint via a
custom knob for clippy.

Closes #ISSUE

Release Notes:

- N/A

crates/ui/src/components/list/list.rs

@@ -13,12 +13,6 @@ pub struct List {
     children: SmallVec<[AnyElement; 2]>,
 }
 
-impl Default for List {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
 impl List {
     pub fn new() -> Self {
         Self {