keystone does not distinguish public and admin endpoints since
Train [1], so there is no need to use a separate endpoint for
keystone admin operations. admin endpoint still can be configured
but there is no functional difference anymore from other endpoints.
We do not need to require admin endpoint and can use an endpoint
specified by OPENSTACK_ENDPOINT_TYPE for all API operations.
This commit reverts commit f9bab3fe19
as we no longer need the workaround.
[1] https://review.opendev.org/c/openstack/keystone/+/664246
Closes-Bug: #1950659
Change-Id: I2660fd2df8081e1d2d9c84626037f94bd9d137a5
35a490f4ec