[VSCode] Remove local feature flag for new `/fix` code actions, enable feature by default

Problem to solve

For the development of [VS Code] Add /fix to code actions (gitlab-org/editor-extensions&127 - closed) a local feature flag was added in [VSCode] Add local feature flag for new `/fix` ... (#1853 - closed). This allow developing the feature iteratively and shipping incomplete work.

This issue is to remove the local feature flag and make the new feature available by default.

Proposed solution

Remove the local feature flag and all checks.