1.0.5 wheel incorrectly requires weakrefmethod on all versions of python

[sparrowt]

Problem

Installing mixbox==1.0.5 on python 3 from PyPI, the mixbox wheel incorrectly tries to bring in weakrefmethod despite this not being actually required.

Unzipping the published wheels I see the following which is missing the python_version condition:
mixbox-1.0.5.dist-info/METADATA: (1.0.4 is broken in the same way too)

Requires-Dist: weakrefmethod (>=1.0.3)

An older wheel (1.0.3) has it correctly as follows
mixbox-1.0.3.dist-info/METADATA:

Requires-Dist: weakrefmethod>=1.0.3; python_version < "3.4"

Possible cause

I see in setup.cfg that it still has the correct python_version constraint: https://github.com/CybOXProject/mixbox/blob/v1.0.5/setup.cfg#L18
but there's also this auto-detection in setup.py: https://github.com/CybOXProject/mixbox/blob/v1.0.5/setup.py#L43
so perhaps that's what is causing the issue, if the 1.0.5 wheel was built using an older version of python (< 3.4)?

It doesn't seem right to me that the wheel's Requires-Dist should be affected by the version of python used at build time, given you're publishing a py2.py3-none-any wheel.

Effects

As a result of this for now I'm forced to install from source using e.g. mixbox-1.0.5.tar.gz in order to avoid unnecessarily installing weakrefmethod when it isn't required. Because I'm in a deliberately constrained environment which only has the necessary wheels on-disk (and stops pip from accessing the internet) the manifestation of this issue for me is as follows:

ERROR: Could not find a version that satisfies the requirement weakrefmethod>=1.0.3 (from mixbox)
ERROR: No matching distribution found for weakrefmethod>=1.0.3

though for many I guess it would just silently install the unnecessary wheel.