Delete | operator for Subprocess::Options

Delete | operator for Subprocess::Options

Summary:
This operator is WRONG. It has not worked correctly for years, e.g. it lacks support for chdir, and several other options.

The operator is not really useful after C++11. Usually, you should just chain setters, e.g. `Subprocess::Options().pipeStdout().pipeStderr()`. If you must repeatedly mutate options in a fixed way, in the C++11 world you can use a lambda instead.

Reviewed By: yfeldblum

Differential Revision: D4862698

fbshipit-source-id: a2d8ace53424b9232e178cf202cf51beb7b59b12