Remove "New Java File" submenu, etc. from Explorer context menu

[tsmaeder]

This extension contributes a submenu "New Java File" and other commands like "New Java Package, etc." to the explorer context menu. I don't think this is consistent with the VS Code UI style: you won't see "New Typescript File" when editing a typescript project, for example. What's more, these menus clutter the context menu even in workspaces that are not Java-related at all.

• For creating new FIles, there is the file/newFilemenu (which is already contributed to)
• Creating a new package is just creating folders and there is already support for that (you can just type in foo/bar in order to create a hierarchy
• Creating a Java project is not context dependent and therefore should not be in a context menu: VS Code uses the command palette for this.
• The "Create Java Project" command is contributed to the file/newFile menu, which again, IMO, goes against VS Code custom.