Checking major version is not needed

[yuanying]

In magnum/api/controllers/base.py, major version is checked and raises NotAcceptable error if major version is mismatched.
But it isn't needed because it is also checked at magnum/api/controllers/v1/__init__.py.

https://github.com/openstack/magnum/commit/9e03afa242ff37e4217570540bfdb65145e4cd61#diff-f8189d4945695d9751a78f4813a120b7R221

so this checking is useless.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/190513
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=75d489323e06f3ada178d8ef6ab97a259a2927ae
Submitter: Jenkins
Branch: master

commit 75d489323e06f3ada178d8ef6ab97a259a2927ae
Author: OTSUKA, Yuanying <email address hidden>
Date: Thu Jun 11 15:25:16 2015 +0900

    Remove major version checking

    Raising NotAcceptable is useless if major version is different, because major
    version is checked by controller itself.

    Change-Id: Ie53af7c511b436459c9bb35e34f32ec2f3cef4f6
    Closes-Bug: #1464113