fix clippy (#10659)

This pr fix clippy warnings in latest clippy version(1.72.0):

Unfortunally it's not easy to handle for [try
fold](https://rust-lang.github.io/rust-clippy/master/index.html#/manual_try_fold)
warning in `start command`

Refer to known issue:
> This lint doesn’t take into account whether a function does something
on the failure case, i.e., whether short-circuiting will affect
behavior. Refactoring to try_fold is not desirable in those cases.

That's the case for our code, which does something on the failure case.

So this pr is making a little refactor on `try_commands`.

crates/nu-command/src/debug/explain.rs

@@ -90,7 +90,6 @@ pub fn get_pipeline_elements(
             let value_span = value.span();
             let value_span_start = value_span.start as i64;
             let value_span_end = value_span.end as i64;
-            let command_name = command_name;
 
             let record = record! {
                     "cmd_index" => Value::string(index, span),