Tests dir no longer need copy of charmhelpers

Charmhelpers is now installed via pip for unit tests so stop
'Make sync' from pulling it down.

Change-Id: I9d3198b419cefbcf7ee710dfbda57415e2a70ff9

Makefile

@@ -18,7 +18,6 @@ bin/charm_helpers_sync.py:
 
 sync: bin/charm_helpers_sync.py
 	@$(PYTHON) bin/charm_helpers_sync.py -c charm-helpers-hooks.yaml
-	@$(PYTHON) bin/charm_helpers_sync.py -c charm-helpers-tests.yaml
 
 publish: lint test
 	bzr push lp:charms/swift-storage

charm-helpers-tests.yaml

@@ -1,7 +0,0 @@
-repo: https://github.com/juju/charm-helpers
-destination: tests/charmhelpers
-include:
-    - contrib.amulet
-    - contrib.openstack.amulet
-    - core
-    - osplatform