Why JQuery 2.x was removed since jquery_update-7.x-3.0-alpha2?
Version 2.1 has not been removed; its files are still present in the 7.x-3.x-dev development snapshot.
What eventually was done is updating the version 2.1 files to version 2.1.4, since they don't keep multiple 2.1.x versions (e.g. 2.1.0, 2.1.1., 2.1.3).