Remove deprecrated [rbac] config group

This PS removes the deprecated [rbac] config group. It was replaced
last release cycle with the [patrole] config group, which has
the exact same options. This is because [patrole] is more user-friendly
and congruent with the project name.

Change-Id: Id1a7af0445bd50f44ddcc4277f952391968726b8
diff --git a/doc/source/usage.rst b/doc/source/usage.rst
index dff43f2..14c2cc7 100644
--- a/doc/source/usage.rst
+++ b/doc/source/usage.rst
@@ -4,8 +4,8 @@
 Usage
 ========
 
-RBAC (API) Tests
-================
+Patrole (API) Tests
+===================
 
 If Patrole is installed correctly, then the RBAC tests can be executed
 from inside the tempest root directory as follows::
@@ -28,7 +28,7 @@
 ..
 
 To change the role that the patrole tests are being run as, edit
-``rbac_test_role`` in the ``rbac`` section of tempest.conf: ::
+``rbac_test_role`` in the ``patrole`` section of tempest.conf: ::
 
     [patrole]
     rbac_test_role = Member