I recently ran into an issue where the "Remove Component" button was grayed out disabled in Experience Editor on a Sitecore 9.0 Update 2 instance. Here are some things you should verify if you experience this behavior:
- Check to make sure the rendering you are trying to remove is marked as editable.
- Check to make sure the placeholder you are trying to remove a component from is marked as editable in placeholder settings.
- Ensure the rendering is added to the placeholder settings "Allowed Controls" field.
- Check to see if there's any non-rendering items inside the placeholder settings "Allowed Controls."
In my situation, it was the last one in the list. The "Layout" Sitecore item had accidentally been added to the placeholder settings "Allowed Controls" and it was breaking several parts of Experience Editor.
There's some additional discussion on this issue here.