Always use EE as the top-level module

We should always use EE as the top-level module to be consistent and avoid needing to use ::EE to resolve ambiguity. We currently have the following offenders:

• Emails::EE
• Banzai::ReferenceParser::EE
• Gitlab::Email::Handler::EE

QA::EE is excluded because it's consistent there.

The following discussion from !5752 (merged) should be addressed:

• @rspeicher started a discussion: (+1 comment)

  Should we use ::EE:: so we're sure we're getting the top-level namespace (throughout)?`