Kill _th_fill binding, which isn't used anymore. (#28511)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28511
We still keep the function in TH, since it's called from within TH.
Test Plan: Imported from OSS
Differential Revision: D18086967
Pulled By: gchanan
fbshipit-source-id: de026fbb076c8bf9d054ed4cf93eba9c7bcfb161
