Require the tf>=2.1 now that crepe dependency is removed and the GPU and CPU/TPU packages have been merged.
Require the tf>=2.1 now that crepe dependency is removed and the GPU and CPU/TPU packages have been merged.

PiperOrigin-RevId: 288925571
Change-Id: I00ffe126e8ad06e1834cc3334d436624b0ba05d6

magenta/ddsp,magenta/ddsp