Original PR description

@Elkasitu @rco-odoo pycompat.reraise had few callsites, and for most `reraise` is needless complexity since P3 chains exceptions by default.

There is one callsite where things are a bit less trivial, but I think removing reraise still makes things *better* (nb: reraising the exception object itself also works but see commit messages for rationale, and note that per its original comment _handle_exception can be called from outside of an `except` block which is why a plain `raise` doesn't work).

Also removed unused `collections` import and outdated comment from pycompat.