Use nightly clippy to kill dead code/fix style (#12334)

- **Remove duplicated imports**
- **Remove unused field in `CompletionOptions`**
- **Remove unused struct in `nu-table`**
- **Clarify generic bounds**
- **Simplify a subtrait bound for `ExactSizeIterator`**
- **Use `unwrap_or_default`**
- **Use `Option` directly instead of empty string**
- **Elide unneeded clone in `to html`**

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

@@ -6,9 +6,6 @@ use std::{io::BufReader, path::Path};
 #[cfg(feature = "sqlite")]
 use crate::database::SQLiteDatabase;
 
-#[cfg(feature = "sqlite")]
-use nu_protocol::IntoPipelineData;
-
 #[cfg(unix)]
 use std::os::unix::fs::PermissionsExt;