Add removeAttribute to `ClassType` (#28984)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28984
Support removing an attribute in `ClassType`, `ClassType` is
considered as a low level API and user of this function
need to guarantee the safety of calling this method.
Test Plan:
tbd
Imported from OSS
Differential Revision: D18253776
fbshipit-source-id: 5814baa3fdf6de6c71d3cc1be225ded9116c961a
