Remove btn-blank class from button.scss

What does this MR do and why?

This MR is split into logical steps in the commits so make it easier to review:

1. Replaces css attributes with util classes in the class to be removed. Important to note here is that I repalces the state overrides with !important so that it will retain this rule while in different states
2. Removes btn-blank override in license-management as it is never referenced, you can verify this by doing a global search for "license-management" and going through its children.
3. find and replace "btn-blank" to the equivalent util classes (slightly more complex in the haml file as it seems like you cant start a class with "!" as easily in HAML
4. Update snapshot tests

This is a clean up only and should have no visual effects

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Related to #497791 (closed)