Remove pins to old py2-supporting versions of ports

Index: requirements.txt
--- requirements.txt.orig
+++ requirements.txt
@@ -1,6 +1,6 @@
-lxml==4.8.0
-pycryptodomex==3.14.1
-construct==2.10.68
-argon2-cffi==21.3.0
-python-dateutil==2.8.2
-future==0.18.2
+lxml
+pycryptodomex
+construct
+argon2-cffi
+python-dateutil
+future