Turn off scalar_check for _th_gather. (#29954)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29954
The underlying op handles scalar_check correctly.
Test Plan: Imported from OSS
Differential Revision: D18548054
Pulled By: gchanan
fbshipit-source-id: a1b44afa80c2928b78abbfba8b8b5d3608ac0fd3
