When uwsgi runs with xml support, it throws the following error on
startup with the latest version of edx-platform:

```
xmlsec.InternalError: (-1, 'lxml & xmlsec libxml2 library version mismatch')
```

See xmlsec/python-xmlsec#320 for more details
on this.

Essentially, the uWSGI wheel is built against a different version of
libxml2 and it causes this version mismach error when trying to load
xmlsec.  The xml support in uWSGI is only needed for runing with xml
configuration files, which tutor does not do.  Following the guidance of
the above issue, I updated the `openedx` Dockerfile to no longer compile
with any xml support as a part of the build. The time to build uWSGI was
only slightly more than building from cache so I'm not concerned about
major slowdowns in the build time for un-cached builds.