.github: Remove confusing on_pull_request variable (#65731)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65731
It originally had purpose but after ciflow was introduced every PR had
on_pull_request set so it's not really as useful as it once was
Also removes the equally as confusing only_build_on_pull_request
variable as well
This change should produce no functional changes in our generated workflows
Signed-off-by: Eli Uriegas <eliuriegas@fb.com>
cc ezyang seemethere malfet pytorch/pytorch-dev-infra
Test Plan: Imported from OSS
Reviewed By: janeyx99
Differential Revision: D31225398
Pulled By: seemethere
fbshipit-source-id: 7bd8e8175794ab7d09b0632321bf52538435e858
