In MR, View file @ should use branch rather than SHA

Description

• Update the View. @ button in the file view of the mr diff to be just a View button that links to the file at the branch (and not at the commit).
• Remove the Edit button from the file view.

Original descripton

I'm not positive of the implications of this, but I've often found myself looking at an MR, then clicking on View file @ somesha, then wanting to edit the file to be told . Perhaps the button to view the file should go to the branch ref instead of the SHA? Going to a specific SHA is more valuable if I'm looking at historic changes, not current changes.