Remove unnecessary echo uses from examples (#7500)

`echo` tends to confuse new Nu users; they expect it to work like
`print` when it just passes a value to the next stage of the pipeline.

We haven't quite figured out what to do about `echo` in the long run,
but I think a good start is to remove `echo` from command examples where
it would be unnecessary and arguably unidiomatic.

crates/nu-command/src/conversions/into/duration.rs

@@ -65,7 +65,8 @@ impl Command for SubCommand {
         vec![
             Example {
                 description: "Convert string to duration in table",
-                example: "echo [[value]; ['1sec'] ['2min'] ['3hr'] ['4day'] ['5wk']] | into duration value",
+                example:
+                    "[[value]; ['1sec'] ['2min'] ['3hr'] ['4day'] ['5wk']] | into duration value",
                 result: Some(Value::List {
                     vals: vec![
                         Value::Record {