hide diff file header section when showing diff of file selected in Files section

### Is your feature request related to a problem? Please describe.
When I select a file in Files section the diff shown in main view contains first five lines about the file header. I want an option to remove this to save five lines
and I obviously know which file I am looking at

### Describe the solution you'd like
remove file header in diff when showing diff for file in Files section

### Describe alternatives you've considered
none