Fix #560

Description

Remove unused $_SESSION['getInfo']
and replace $_SESSION['aid'] with CUserManager->GetAid()

Motivation and Context

$_SESSION['aid'] is defunct with #554

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.