Remove no longer needed CRYPTOGRAPHY_ALLOW_OPENSSL_102 environment variable

[lsd-cat]

SecureDrop has dropped support of Xenial in #5725

As described in the cryptography documentation, the CRYPTOGRAPHY_ALLOW_OPENSSL_102 was used to force compatibility between cryptography==3.2 and OpenSSL 1.0.2.
The current version of OpenSSL in Focal is in the 1.1 branch and also cryptography is now pinned to the cryptography>=3.4.7 version.

The description of the original compatibility issue is here https://cryptography.io/en/3.2/faq/
The commit of the original change is here 4569657

Status

Ready for review

Description of Changes

Dropping the flag should have no effect on any supported system.

Testing

A normal test run in staging and prod, if any function that uses the cryptography module works, then everything should be working as usual.

Checklist

My staging environment is currently undergoing other disruptive testing and thus I have not run the infra tests yet.

• Configuration tests pass

• These changes do not require documentation

[zenmonkeykstop]

Tested in staging, no issues with any crypto-related functionality. LGTM