Remove unneeded $logger property in Session

[paulbalandan]

Description
Session already imports the $logger property through the use of LoggerAwareTrait. So this declaration is redundant.

Moreover, if a user accidentally uses v2 or v3 of psr/log, like here which I think what happened, this will cause an incompatible declaration error.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide