[Lens] Fixes edit configuration flyout display (elastic#165675)

## Summary


Fixes a problem on the flyout ui (the black line on the right). I dont
think that this line is useful. Vertical scrolling works fine.

**Before**

<img width="1435" alt="image"
src="https://github.com/elastic/kibana/assets/17003240/56868893-2aad-4118-a5c6-245b1111b735">


**Now**

<img width="1356" alt="image"
src="https://github.com/elastic/kibana/assets/17003240/0f2d0e87-d60d-4507-8d68-accc0ba840ed">

x-pack/plugins/lens/public/app_plugin/shared/edit_on_the_fly/lens_configuration_flyout.tsx

@@ -100,8 +100,8 @@ export function LensEditConfigurationFlyout({
       <EuiFlyoutBody
         className="lnsEditFlyoutBody"
         css={css`
-          // styles needed to display extra drop targets that are outside of the config panel main area while also allowing to scroll vertically
-          overflow-y: scroll;
+          // styles needed to display extra drop targets that are outside of the config panel main area
+          overflow-y: auto;
           padding-left: ${euiThemeVars.euiFormMaxWidth};
           margin-left: -${euiThemeVars.euiFormMaxWidth};
           pointer-events: none !important;