Simplify installation of test deps

Pip >=6 can handle the functionality of filtering dependencies
within a single requirements files instead of needing to shim
this functionality in externally.

requirements.txt

@@ -4,3 +4,4 @@
 nose==1.3.3
 mock==1.3.0
 wheel==0.24.0
+unittest2==0.5.1; python_version == '2.6'

scripts/ci/install

@@ -13,16 +13,6 @@ os.chdir(REPO_ROOT)
 def run(command):
     return check_call(command, shell=True)
 
-
-try:
-    # Has the form "major.minor"
-    python_version = os.environ['PYTHON_VERSION']
-except KeyError:
-    python_version = '.'.join([str(i) for i in sys.version_info[:2]])
-
-if python_version == '2.6':
-    run('pip install -r requirements26.txt')
-
 run('pip install -r requirements.txt')
 run('pip install coverage')
 if os.path.isdir('dist') and os.listdir('dist'):