Use Backblaze Uninstaller to uninstall

Rather than having to manually delete the various applications,
preference panes and `launchctl` jobs installed by the Backblaze
Installer ourselves, use the included Backblaze Uninstaller script
instead.

Note that the Uninstaller will not delete user-specific files so we
retain the existing zap stanza.

Casks/backblaze.rb

@@ -8,14 +8,7 @@
 
  installer manual: "Backblaze Installer.app"
 
- uninstall launchctl: [
- "com.backblaze.bzserv",
- "com.backblaze.bzbmenu",
- ],
- delete: [
- "#{appdir}/Backblaze.app",
- "/Library/PreferencePanes/BackblazeBackup.prefPane",
- ]
+ uninstall script: "#{staged_path}/Backblaze Uninstaller.app/Contents/MacOS/Backblaze Uninstaller"
 
  zap trash: [
  "/Library/Backblaze.bzpkg",