[IDE] Remove linked files from project

[ketttY]

• For linked files only provide "Remove" (bound with cmd + delete shortcut) like VS Win

  VS Win:

  

Fixes: https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1026629/

[mrward]

Still seems to be some discussion from the design team about the behaviour here - I guess after this code change was made.

[ketttY]

@mrward Oops... Just saw that :) Thanks for the heads-up, adding do-not-merge label for now

[ketttY]

@monojenkins rebase