Blockstore and all of its (experimental) functionality has been replaced with
openedx-learning, aka "Learning Core". This commit uninstalls the now-unused
openedx-blockstore package and removes all dangling references to it.
Note: This also removes the `copy_library_from_v1_to_v2` management command,
which has been broken ever since we switched from Blockstore to Learning Core.
Part of this DEPR: https://github.com/openedx/public-engineering/issues/238
Now that the content in `guides` is all of the edx-platform docs, move
them all into the top-level docs directory to reduce confusion.
BREAKING CHANGE: Guides are now just docs. This will require updating
the publishing settings so that RTD looks for the conf in a different
location.
