make vector_norm backward call norm_backward (#59135)
Summary:
Per title. Remove duplicated code.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59135
Reviewed By: mruberry
Differential Revision: D28775716
Pulled By: ngimel
fbshipit-source-id: 50dc77590db15976453fc41c3657a77198749849
