Remove testcase test_invalid_auth_version_request

In keystoneclient/middleware/auth_token.py, _choose_api_version(), the
codes's logic assume that auth_version in conf is always correct, so the
testcase test_invalid_auth_version_request() is incorrect. This patch
remove it.

Fixes bug #1218881

Change-Id: I6aec0526a6a60eea8d357ec1b44570e7d74da653