pbr is used only at build time
argparse is in the standard library
six is used only in examples
https://bugs.gentoo.org/show_bug.cgi?id=546776
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,6 +2,3 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
-pbr>=0.6,!=0.7,<1.0
-argparse
-six>=1.7.0