What is RemoteSystemsTempFiles in Eclipse?

If you want to remove the RemoteSystemsTempFiles, just go under Window -> Preferences -> General -> Startup and Shutdown and uncheck "RSE UI". Then you can remove the folder and eclipse won't recreate it.

You can delete it if you wish, it doesn't do any harm to other projects. It is created by the remote systems explorer that comes with eclipse.

In Window->preferences type 'remote'. Click on remote systems view and uncheck the box that says 'reopen remote systems view to previous state'.

Eclipse already adds the .metadata folder - why does it add extra clutter?

If you're still seeing unwanted results in RemoteSystemsTempFiles when searching for a resource (e.g. CTRL+SHIFT+R), you can manually show the Eclipse resource in the Project Explorer and remove it...

Project Explorer view > Customize View... > Filters > Uncheck "RSE Internal Projects" > OK > find it in the Project Explorer tree > expand it > remove old folders.

You'll need to remove the Remote System Explorer End-User Runtime package.
Help > Installation Details > Installed Software and scroll down until you see it.

It has several sub-packages, all of which are removed altogether with their parent package.