Cryptography version update (#4568)

* Update required cryptography library version

* remove old env variable from dockerfile

- Was required when we based on alpine linux
- now we use python_slim

* Fix file contents

Dockerfile

@@ -19,9 +19,6 @@ ARG commit_tag=""
 
 ENV PYTHONUNBUFFERED 1
 
-# Ref: https://github.com/pyca/cryptography/issues/5776
-ENV CRYPTOGRAPHY_DONT_BUILD_RUST 1
-
 ENV INVENTREE_LOG_LEVEL="WARNING"
 ENV INVENTREE_DOCKER="true"