Drop python-cinderclient usage

We've switched everything to python-openstackclient and therefore
the usage of python-cinderclient is no longer necessary.

Change-Id: I27d1b675f422aeb07ffdf41ea945a83121f562cf

lower-constraints.txt

@@ -70,7 +70,6 @@ pyOpenSSL==17.5.0
 pyparsing==2.2.0
 pyperclip==1.6.0
 python-ceilometerclient==2.5.0
-python-cinderclient==3.5.0
 python-dateutil==2.7.0
 python-glanceclient==2.9.1
 python-keystoneclient==3.15.0