refactor: Completely remove Blockstore (#34739)

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

lms/envs/devstack.py

@@ -262,9 +262,6 @@ TOKEN_SIGNING.update({
     )
 })
 
-############################### BLOCKSTORE #####################################
-BLOCKSTORE_API_URL = "http://edx.devstack.blockstore:18250/api/v1/"
-
 ########################## PROGRAMS LEARNER PORTAL ##############################
 LEARNER_PORTAL_URL_ROOT = 'http://localhost:8734'