Simplify `_is_broken_pipe_error` definition
Simplify `_is_broken_pipe_error` definition

The different-definition-based-on-platform is unnecesary. This isn't
called such that the cost of an additional conditional matters much.

Bundling it into a single function definition makes it easier to read.

pypa/pip,sbidoul/pip,pradyunsg/pip,sbidoul/pip,pfmoore/pip,pradyunsg/pip,pfmoore/pip,pypa/pip