Remove brackets.app.abortQuit checks

[le717]

Removes the two year old brackets.app.abortQuit checks added before the switch to the CEF3 shell. Fixes #7883.

[busykai]

@le717, if you don't mind, could you please sign Brackets CLA? Otherwise this PR cannot be merged.

[le717]

I signed it already, as can be checked here. The Travis build failed because there were too many GitHub API requests. Do I need to sign it again?

[busykai]

You're right -- haven't read the actual server response. No, you don't to sign it again.

[busykai]

@le717, Brackets does not run only in brackets-shell, there are other uses as well, so it is slightly more complicated...

@JeffryBooher, in principle, there should be no problem merging this request. Other brackets.app calls are not protected this way, so an implementation of application should implement entire contract anyways. I'm thinking perhaps #6605 should be changed to actually define and document the interface in javascript (currently it could only be found in adobe/brackets-shell and nowhere in adobe/brackets itself).

[redmunds]

Looks good. Merging.