tests: removed 'retargetable' framework

I am not 100% sure what that is but it seems like an experiment that
never gave fruits. Since the introduction of the code, we had huge
changes in how we test api, we got tempest plugins, we steadily move
from api testing in unit tests, we have fullstack, etc.

I assume if I can't understand what's use of that, then it's probably
irrelevant code, and so it's better to clean it from the tree.

Change-Id: I0b1be0c761da75885981952a4f5ab5a43bc09525
diff --git a/neutron/tests/tempest/README.rst b/neutron/tests/tempest/README.rst
index d61e72c..f27c34e 100644
--- a/neutron/tests/tempest/README.rst
+++ b/neutron/tests/tempest/README.rst
@@ -1,10 +1,9 @@
 WARNING
 =======
 
-The files under this path were copied from tempest as part of the move
-of the api tests, and they will be removed as required over time to
-minimize the dependency on the tempest testing framework.
-While it exists, only neutron.tests.tempest.api and neutron.tests.retargetable
-should be importing files from this path.  neutron.tests.tempest.config uses
-the global cfg.CONF instance and importing it outside of the api tests
-has the potential to break Neutron's use of cfg.CONF.
+Some files under this path were copied from tempest as part of the move of the
+api tests, and they will be removed as required over time to minimize the
+dependency on the tempest testing framework.  While it exists, only
+neutron.tests.tempest.* should be importing files from this path.
+neutron.tests.tempest.config uses the global cfg.CONF instance and importing it
+outside of the api tests has the potential to break Neutron's use of cfg.CONF.