feat!: remove olx_importer app

This was never published as part of the openedx-core package, and
existed as an early way to bring XBlock component data into our models
for testing purposes. Now that backup_restore exists and we have
alternate ways to import content via the UX as well (from v1 libraries
and courses), there's no point in keeping olx_importer around and up to
date.

Author: ormsbee

README.rst

@@ -55,7 +55,6 @@ Code Overview
 * ``./src/``: All published code. Packages are importable relative to this directory (e.g., ``import openedx_content``). See ``readme.rst`` in each sub-folder.
 * ``./tests/``: Unit tests (not published).
 * ``./test_utils/``: Internal helpers for unit tests (not published).
-* ``./olx_importer/``: Internal utility for importing data for development (not published).
 
 License
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