run-tests: remove references to Python 2.6

These are the obvious ones. There is tons of code in this file
implementing features from unittest that weren't present in
Python 2.6. But that's for other patches.

tests/run-tests.py

@@ -90,7 +90,7 b' if sys.version_info > (3, 5, 0):'
         return p.decode('utf-8')
 
 elif sys.version_info >= (3, 0, 0):
-    print('%s is only supported on Python 3.5+ and 2.6-2.7, not %s' %
+    print('%s is only supported on Python 3.5+ and 2.7, not %s' %
           (sys.argv[0], '.'.join(str(v) for v in sys.version_info[:3])))
     sys.exit(70) # EX_SOFTWARE from `man 3 sysexit`
 else:
@@ -317,7 +317,7 b' def getparser():'
     parser.add_option("--ipv6", action="store_true",
                       help="prefer IPv6 to IPv4 for network related tests")
     parser.add_option("-3", "--py3k-warnings", action="store_true",
-        help="enable Py3k warnings on Python 2.6+")
+        help="enable Py3k warnings on Python 2.7+")
     # This option should be deleted once test-check-py3-compat.t and other
     # Python 3 tests run with Python 3.
     parser.add_option("--with-python3", metavar="PYTHON3",
@@ -435,7 +435,7 b' def parseargs(args, parser):'
     if options.py3k_warnings:
         if PYTHON3:
             parser.error(
-                '--py3k-warnings can only be used on Python 2.6 and 2.7')
+                '--py3k-warnings can only be used on Python 2.7')
     if options.with_python3:
         if PYTHON3:
             parser.error('--with-python3 cannot be used when executing with '