handle {self} when recursively removing node from UseTree

This commits adds logic to `UseTree::remove_recursive` to handle converting
`use x::y::{self};` to `use x::y;` when recurisevly removing nodes. For example
`use x::y::{self, Z};` can become `use x::y` if `Z` is unused.

crates/ide-assists/src/handlers/remove_unused_imports.rs

@@ -800,7 +800,7 @@ mod z {
 }
 
 mod z {
-    use super::inner::{self};
+    use super::inner;
 
     fn f() {
         let y = inner::Y();

crates/syntax/src/ast/edit_in_place.rs

@@ -451,13 +451,21 @@ impl ast::UseTree {
                 u.remove();
             }
         } else if let Some(u) = parent.and_then(ast::UseTreeList::cast) {
-            if u.use_trees().next().is_none() {
+            if u.is_just_self() {
+                let parent = u.syntax().parent().and_then(ast::UseTree::cast);
+                if let Some(u) = parent {
+                    let path = u.path().unwrap();
+                    ted::remove_all_iter(u.syntax().children_with_tokens());
+                    ted::insert_raw(Position::first_child_of(u.syntax()), path.syntax());
+                }
+            } else if u.use_trees().next().is_none() {
                 let parent = u.syntax().parent().and_then(ast::UseTree::cast);
                 if let Some(u) = parent {
                     u.remove_recursive();
                 }
+            } else {
+                u.remove_unnecessary_braces();
             }
-            u.remove_unnecessary_braces();
         }
     }