[Java] @Deprecated annotation fix

[brian-byungsookim]

Description

OAS 2.0 supports deprecated methods, and the Java libraries should reflect that. There was a previous PR related to this, but that didn't include the actual Java @Deprecated method annotations.

Swagger-codegen version

2.3.0

Related issues/PRs

#6166

Suggest a fix/enhancement

Will submit a PR fixing this.

[wing328]

Fixed via #6801