Don't allow formatters in format on save (#39400)

Closes #ISSUE



Release Notes:

- settings: Removed support for having format steps in both the
`format_on_save` and `formatter` settings for languages.
`format_on_save` is now restricted to the values of `"on"` and `"off"`,
and all format steps should be set under the `formatter` key. If you
were using `format_on_save` but not `formatter` this will be migrated
for you, otherwise it will require a manual migration.

---------

Co-authored-by: Smit <smit@zed.dev>

crates/project/src/lsp_store.rs

@@ -1366,7 +1366,6 @@ impl LocalLspStore {
 
         let formatters = match (trigger, &settings.format_on_save) {
             (FormatTrigger::Save, FormatOnSave::Off) => &[],
-            (FormatTrigger::Save, FormatOnSave::List(formatters)) => formatters.as_ref(),
             (FormatTrigger::Manual, _) | (FormatTrigger::Save, FormatOnSave::On) => {
                 match &settings.formatter {
                     SelectedFormatter::Auto => {