This PR corrects an issue where make clean was not removing the .dmg
$make clean now works as expected.
$make deploy still works as expected.
cleans Bitcoin-Qt.dmg, background.tiff bachground.png, background@2x.png as expected.
old config
new config

The change was added to documentation but make clean needed to be updated.
https://github.com/bitcoin/bitcoin/commit/4441e58497513cc55cfebfdcaaeee340f62f8062#diff-9de36befe13356841c2699ee0eff4a0aR14
The old config named the Bitcoin-Core.dmg based on the PACKAGE_NAME variable (which is still used for naming the Bitcoin Core.app (with space)).