KAFKA-8962: Use least_loaded_node() for describe_topics()
KAFKA-8962: Use least_loaded_node() for describe_topics()

In KAFKA-8962 the `AdminClient.describe_topics()` call was changed from
using the controller to using the `least_loaded_node()`:
https://github.com/apache/kafka/commit/317089663cc7ff4fdfcba6ee434f455e8ae13acd#diff-6869b8fccf6b098cbcb0676e8ceb26a7R1540

As a result, no metadata request/response processing needs to happen
through the controller, so it's safe to remove the custom
error-checking. Besides, I don't think this error-checking even added
any value because AFAIK no metadata response would return a
`NotControllerError` because the recipient broker wouldn't realize the
metadata request was intended for only the controller.

Originally our admin client was implemented using the least-loaded-node,
then later updated to the controller. So updating it back to
least-loaded node is a simple case of reverting the associated commits.

This reverts commit 7195f0369c7dbe25aea2c3fed78d2b4f772d775b.

This reverts commit 6e2978edee9a06e9dbe60afcac226b27b83cbc74.

This reverts commit f92889af79db08ef26d89cb18bd48c7dd5080010.

ohmu/kafka-python,ohmu/kafka-python,DataDog/kafka-python,dpkp/kafka-python,scrapinghub/kafka-python,mumrah/kafka-python,scrapinghub/kafka-python,mumrah/kafka-python,dpkp/kafka-python