[optimizer] refactor Adadelta to use functional API (#50409)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50409
Test Plan: Imported from OSS
Reviewed By: izdeby
Differential Revision: D25932780
Pulled By: wanchaol
fbshipit-source-id: 2fc025f66a0e0863f21689892e19d8a5681f2f2f
