Remove the unused coding style modules

Python modules related to coding style checks (listed in blacklist.txt in
openstack/requirements repo) are dropped from lower-constraints.txt
as they are not actually used in tests (other than pep8).

more info: https://github.com/openstack/requirements/blob/master/blacklist.txt

Change-Id: I333bbddf70a4ead1778813a8311969ec372604d3

lower-constraints.txt

@@ -2,7 +2,6 @@ amqp==2.1.1
 appdirs==1.3.0
 asn1crypto==0.23.0
 Babel==2.3.4
-bandit==1.4.0
 cachetools==2.0.0
 cffi==1.14.0
 cliff==2.8.0
@@ -19,13 +18,11 @@ eventlet==0.18.2
 extras==1.0.0
 fasteners==0.7.0
 fixtures==3.0.0
-flake8==2.5.5
 future==0.16.0
 futurist==1.2.0
 gitdb==0.6.4
 GitPython==1.0.1
 greenlet==0.4.15
-hacking==1.1.0
 idna==2.6
 iso8601==0.1.11
 Jinja2==2.10
@@ -37,7 +34,6 @@ keystoneauth1==3.5.0
 kombu==4.0.0
 linecache2==1.0.0
 MarkupSafe==1.1.1
-mccabe==0.2.1
 monotonic==0.6
 msgpack-python==0.4.0
 munch==2.1.0
@@ -62,14 +58,12 @@ paramiko==2.0.0
 Paste==2.0.2
 PasteDeploy==1.5.0
 pbr==2.0.0
-pep8==1.5.7
 pika==0.10.0
 pika-pool==0.1.3
 positional==1.2.1
 prettytable==0.7.2
 pyasn1==0.1.8
 pycparser==2.18
-pyflakes==0.8.1
 pyinotify==0.9.6
 pyOpenSSL==17.1.0
 pyparsing==2.1.0