[REM] python-stdnum from requirements

It is never used in the code, and causes problems with wheels: related
to pypa/pip#2105

closes #3744

requirements.txt

@@ -26,7 +26,6 @@ pyserial==2.7
 python-dateutil==1.5
 python-ldap==2.4.15
 python-openid==2.2.5
-python-stdnum==0.9
 pytz==2014.4
 pyusb==1.0.0b1
 qrcode==5.0.1