Update MultiRegional and Regional to Standard

[JesseLovelace]

Previously, we implemented the concept of "Location Type" to move the concept of bucket location away from storage class. It is no longer considered correct to use "MultiRegional" or "Regional" as a storage class, instead those should be location types.

As such, we need to update every instance of the "MultiRegional" and "Regional" storage in samples, library documentation, and tests to use "Standard" instead--Standard is a correct storage class.

Note that "MultiRegional" and "Regional" should only be replaced with "Standard" in cases where they are used a storage class. If they're used as a location type, that's fine and doesn't need to be replaced.

https://github.com/googleapis/google-cloud-python/blob/ae2e7058e402c4c963bc4991af7cd5f2b2801cc9/storage/tests/unit/test_bucket.py

google-cloud-python/storage/tests/unit/test_blob.py

Line 3040 in ccac1e1

storage_class = "MULTI_REGIONAL"

google-cloud-python/storage/tests/unit/test_bucket.py

Line 55 in ae2e705

self.assertEqual(conditions.matches_storage_class, ["REGIONAL"])

https://github.com/GoogleCloudPlatform/python-docs-samples/blob/03e47889042b52ebb2610c5ba19a23bebb39a497/notebooks/rendered/storage-command-line-tool.md#L73
https://github.com/GoogleCloudPlatform/python-docs-samples/blob/03e47889042b52ebb2610c5ba19a23bebb39a497/notebooks/tutorials/storage/Storage%20command-line%20tool.ipynb#L141