install-deps.sh: use latest setuptools

install-deps.sh: use latest setuptools

this change reverts "install-deps.sh: workaround setuptools' dependency on six"

This reverts commit 30ce5e55460e333e1240704112a16fae68b3325f.

tl;dr: this change addresses the failures of "make check" runs on arm64
builders when they try to build `mgr-dashboard-test-venv` target.

long story: without this change, we will fail to pull in
setuptools >= 36, and as a result pip will fail to import
`setuptools.build_meta` in `pip/_vendor/pep517/_in_process.py`. and will
a `BackendUnavailable` exception thrown by `_call_hook()` in
`pip/_vendor/pep517/wrappers.py`. since the issue addressed by 30ce5e55
has been addressed since setuptools >= 36.0.1, we should be safe to
upgrade to the latest setuptools now.

Signed-off-by: Kefu Chai <kchai@redhat.com>