Unpin openedx-core in edx-platform

[huniafatima-99]

openedx-learning is pinned at openedx-learning==0.10.1 due to the reason that it's under development and no major updates should happen during that.
If the development is complete we can remove this constraint and close this issue

[kdmccormick]

Update for Verawood:

We've loosened the constraint to just openedx-core<2. We'd still like to manage the upgrade of breaking changes in openedx-platform.