Minor manual cleanu

* use default derive
* use `strip_prefix` where possible to avoid dup work

crates/vfs/src/file_set.rs

@@ -140,16 +140,11 @@ impl FileSetConfig {
 }
 
 /// Builder for [`FileSetConfig`].
+#[derive(Default)]
 pub struct FileSetConfigBuilder {
     roots: Vec<Vec<VfsPath>>,
 }
 
-impl Default for FileSetConfigBuilder {
-    fn default() -> Self {
-        FileSetConfigBuilder { roots: Vec::new() }
-    }
-}
-
 impl FileSetConfigBuilder {
     /// Returns the number of sets currently held.
     pub fn len(&self) -> usize {

crates/vfs/src/path_interner.rs

@@ -9,16 +9,11 @@ use rustc_hash::FxHasher;
 use crate::{FileId, VfsPath};
 
 /// Structure to map between [`VfsPath`] and [`FileId`].
+#[derive(Default)]
 pub(crate) struct PathInterner {
     map: IndexSet<VfsPath, BuildHasherDefault<FxHasher>>,
 }
 
-impl Default for PathInterner {
-    fn default() -> Self {
-        Self { map: IndexSet::default() }
-    }
-}
-
 impl PathInterner {
     /// Get the id corresponding to `path`.
     ///