Remove columns from the Workspaces list

What does this MR do and why?

It removes the following columns from the Workspaces list:

• Last used: Adding this column is outside of the Remote Development MVC and we will add it in later iterations: Display workspace creation date in the workspac... (#408119 - closed)
• Branch: Same as last used: Display Workspace’s project repository current ... (#408129 - closed)

It also changes the preview URL column to only be visible when the Workspace’s status is Running Do not display workspace preview URL when works... (#407415 - closed)

Context

The Workspaces UI relies on populating the Apollo Cache with dummy data. We will connect the production GraphQL API in future iterations.

Screenshots or screen recordings

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Enable the remote development feature flag Feature.enable(:remote_development_feature_flag)
2. You might need to run gdk restart rails-web so rails reconfigure the routes.
3. Open http://gdk.test:3000/-/remote_development/workspaces in your Web Browser.
4. You should see a list of workspaces like the screenshots above.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.