Drop support for Python<3.4 in demo code

This version of python reached its EOL in March 2019.

Signed-off-by: Hugo Osvaldo Barrera <hugo@whynothugo.nl>

demos/userns-block-fd.py

@@ -24,9 +24,8 @@ else:
     os.close(pipe_info[0])
     os.close(userns_block[1])
 
-    if sys.version_info >= (3, 4):
+    os.set_inheritable(pipe_info[1], True)
-        os.set_inheritable(pipe_info[1], True)
+    os.set_inheritable(userns_block[0], True)
-        os.set_inheritable(userns_block[0], True)
 
     args = ["bwrap",
             "bwrap",