feat!: assume & remove BLOCKSTORE_USE_BLOCKSTORE_APP_API (#33765)

Originally, Blockstore was an independent micro-service, accessed via a REST API.
Then, we changed Blockstore so it could be installed as an in-process Django app.

To support both modes, there existed a blockstore_api wrapper library in edx-platform,
with toggles controlling whether the wrapper called out to the micro-service's REST API versus the
Django app's Python API. Now that the micro-service Blockstore implementation is deprecated,
though, this wrapper library and toggles are just unnecessary complexity.

As a first step towards cleanup, we:

* remove several toggles and settings (details below);
* remove the blocokstore_api wrapper methods which called the REST API and
  marshalled them back into Python objects; and
* remove all test cases which relied on the Blockstore micro-service (and were skippped in CI).

In the future, we will remove the content libraries indexer, 
clean up the remaining bits of blockstore_api, and flatten out all
the Blockstore-related test class hierarchies which are no longer nceessary.

BREAKING CHANGE:
* These Django settings are removed:
  * BLOCKSTORE_PUBLIC_URL_ROOT
  * BLOCKSTORE_API_URL
  * BLOCKSTORE_API_AUTH_TOKEN
  * BLOCKSTORE_USE_BLOCKSTORE_APP_API
* The blockstore.use_blockstore_app_api Waffle switch is removed.
* edx-platform will act as it did when the DJango setting BLOCKSTORE_USE_BLOCKSTORE_APP_API
  or the Waffle switch blockstore.use_blockstore_app_api were enabled. That is, any running Blockstore
  micro-service instance will be ignored, and the Blockstore package which is installed into edx-platform
  will be used instead.

Ref: https://github.com/openedx/blockstore/issues/296

cms/envs/common.py

@@ -115,7 +115,6 @@ from lms.envs.common import (
     ENTERPRISE_BACKEND_SERVICE_EDX_OAUTH2_PROVIDER_URL,
 
     # Blockstore
-    BLOCKSTORE_USE_BLOCKSTORE_APP_API,
     BUNDLE_ASSET_STORAGE_SETTINGS,
 
     # Methods to derive settings
@@ -2606,8 +2605,7 @@ PROCTORING_BACKENDS = {
 PROCTORING_SETTINGS = {}
 
 ################## BLOCKSTORE RELATED SETTINGS  #########################
-BLOCKSTORE_PUBLIC_URL_ROOT = 'http://localhost:18250'
-BLOCKSTORE_API_URL = 'http://localhost:18250/api/v1/'
+
 # Which of django's caches to use for storing anonymous user state for XBlocks
 # in the blockstore-based XBlock runtime
 XBLOCK_RUNTIME_V2_EPHEMERAL_DATA_CACHE = 'default'

cms/envs/devstack-experimental.yml

@@ -40,8 +40,6 @@ AWS_SES_REGION_ENDPOINT: email.us-east-1.amazonaws.com
 AWS_SES_REGION_NAME: us-east-1
 AWS_STORAGE_BUCKET_NAME: SET-ME-PLEASE (ex. bucket-name)
 BASE_COOKIE_DOMAIN: localhost
-BLOCKSTORE_API_URL: http://localhost:18250/api/v1
-BLOCKSTORE_PUBLIC_URL_ROOT: http://localhost:18250
 BLOCK_STRUCTURES_SETTINGS:
     COURSE_PUBLISH_TASK_DELAY: 30
     TASK_DEFAULT_RETRY_DELAY: 30

cms/envs/test.py

@@ -27,8 +27,6 @@ from .common import *
 
 # import settings from LMS for consistent behavior with CMS
 from lms.envs.test import (  # pylint: disable=wrong-import-order
-    BLOCKSTORE_USE_BLOCKSTORE_APP_API,
-    BLOCKSTORE_API_URL,
     COMPREHENSIVE_THEME_DIRS,  # unimport:skip
     DEFAULT_FILE_STORAGE,
     ECOMMERCE_API_URL,
@@ -184,10 +182,6 @@ CACHES = {
 }
 
 ############################### BLOCKSTORE #####################################
-# Blockstore tests
-RUN_BLOCKSTORE_TESTS = os.environ.get('EDXAPP_RUN_BLOCKSTORE_TESTS', 'no').lower() in ('true', 'yes', '1')
-BLOCKSTORE_API_URL = os.environ.get('EDXAPP_BLOCKSTORE_API_URL', "http://edx.devstack.blockstore-test:18251/api/v1/")
-BLOCKSTORE_API_AUTH_TOKEN = os.environ.get('EDXAPP_BLOCKSTORE_API_AUTH_TOKEN', 'edxapp-test-key')
 BUNDLE_ASSET_STORAGE_SETTINGS = dict(
     STORAGE_CLASS='django.core.files.storage.FileSystemStorage',
     STORAGE_KWARGS=dict(