Remove unnecessary #[allow(...)] annotations (#6870)

* Remove unnecessary `#[allow]` annots

Reduce the number of lint exceptions that are not necessary with the
current state of the code (or more recent toolchain)

* Remove dead code from `FileStructure` in nu-command

* Replace `allow(unused)` with relevant feature switch

* Deal with `needless_collect` with annotations

* Change hack for needless_collect in `from json`

This change obviates the need for `allow(needless_collect)`
Removes a pessimistic allocation for empty strings, but increases
allocation size to `Value`

Probably not really worth it.

* Revert "Deal with `needless_collect` with annotations"

This reverts commit 05aca98445.

The previous state seems to better from a performance perspective as a
`Vec<String>` is lighter weight than `Vec<Value>`

crates/nu-command/src/filesystem/util.rs

@@ -14,20 +14,11 @@ pub struct FileStructure {
     pub resources: Vec<Resource>,
 }
 
-#[allow(dead_code)]
 impl FileStructure {
     pub fn new() -> FileStructure {
         FileStructure { resources: vec![] }
     }
 
-    pub fn contains_more_than_one_file(&self) -> bool {
-        self.resources.len() > 1
-    }
-
-    pub fn contains_files(&self) -> bool {
-        !self.resources.is_empty()
-    }
-
     pub fn paths_applying_with<F>(
         &mut self,
         to: F,