msg.options persists when dropdown options are selected

### Description

> There is a minor bug: In dynamic dropdown, when user selects a dropdown item, the msg.options is also passed through to the dropdown output. This should be removed to improve efficiency. We could have thousands of items in the msg.options.

source: https://discourse.nodered.org/t/dashboard-2-dynamic-dropdown/85727/7?u=joepavitt

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate