add quickaction to remove unused farg name

[ZacLN]

Fixes julia-vscode/julia-vscode#2356

For every PR, please check the following:

• End-user documentation check. If this PR requires end-user documentation in the Julia VS Code extension docs, please add that at https://github.com/julia-vscode/docs.
• Changelog mention. If this PR should be mentioned in the CHANGELOG for the Julia VS Code extension, please open a PR against https://github.com/julia-vscode/julia-vscode/blob/master/CHANGELOG.md with those changes.

[davidanthoff]

Needs a test :)