Remove EditorConfig Extension and Config File

[tsmaeder]

Feature Description:

We now download the EditorConfig extension as part of the download:plugins script. Also, we have a .editorConfig file checked into our repository.
If the editor config extension was just setting preferences, this would not be problematic, but the VS Code extension manipulates file content before saving. This interferes with Theia/VS Code built-in settings like files.insertFinalNewline behavior, leading to confusion. Since we now have Theia IDE, the preferred way to edit the Theia code base is Theia IDE, so we should get rid of the EditorConfig extensions and configuration file.