Remove unused _convolution_nogroup op (#68829)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/68829
Test Plan: Imported from OSS
Reviewed By: zou3519, albanD
Differential Revision: D32627578
Pulled By: jbschlosser
fbshipit-source-id: 8a4c0ac58aae184a465b1fd40cce880a60d67339
