Remove python-heatclient from test-requirements.txt

It seems that it was added back in Liberty where an effort was
started to setup functional tests, however it is not used at the
moment.

This patch removes it from the list of dependencies.  With time,
Tempest should handle all integration checks.

Change-Id: Ieb3a000eda58dcb642cbd099273c91ad355bfb85

test-requirements.txt

@@ -18,7 +18,6 @@ PrettyTable<0.8,>=0.7.1 # BSD
 PyYAML>=3.10.0 # MIT
 python-barbicanclient>=4.0.0 # Apache-2.0
 python-ceilometerclient>=2.5.0 # Apache-2.0
-python-heatclient>=1.6.1 # Apache-2.0
 python-neutronclient>=5.1.0 # Apache-2.0
 python-openstackclient>=3.3.0 # Apache-2.0
 python-swiftclient>=3.2.0 # Apache-2.0