elgg_unextend_view doesn't have a third argument, so it's just
But, in order for that to work you need to make sure it's executed *after* hypeWall has registered it. If you unregister it, and then hypeWall registers it then it will be registered. I assume this is registered in the init function of hypeWall, so you should put this in the init function of your own plugin, and make sure that plugin is below hypeWall on the plugin list.
Physical presence of the vie file is not mandatory. Even if the file for the view doesn't exist, you can still extend it using the api - elgg_extend_view()
If you want to remove the group file widget then
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