RFR: JDK-8231281: Consider eliminating --identifier option

[Alexander Matveev]

Please review the jpackage fix for bug [1] at [2].

This is a fix for the JDK-8200758-branch branch of the open sandbox 
repository (jpackage).

- Removed --identifier option, since it only usage is to specify 
identifier when generating pkg on macOS and as default value for 
--mac-package-identifier.
- Specifying identifier is no longer needed when generating pkg from app 
image and it will be extract from app image by default. 
--mac-package-identifier can be used to overwrite default value.
- Removed check for identifier from DMG bundler, since it is not 
required by DMG.

[1] https://bugs.openjdk.java.net/browse/JDK-8231281

[2] http://cr.openjdk.java.net/~almatvee/8231281/webrev.00/

Thanks,
Alexander