change our manylinux1 and macos wheel builders to build limited api (#4113)

* change our manylinux1 and macos wheel builders to build limited api

pip does not currently support the--py-limited-api cli flag that wheel
uses so we have to switch to downloading and then building via
setup.py bdist_wheel for now.
However, we can get rid of everything but the py34 builder on
mac/linux/linux32, saving us 6 wheels now (and soon 9 with the release
of python 3.7)

* some newlines

* review feedback
1 file changed