refactor: remove verification-specific APIs from Java SDK

[portal-wheatley]

Summary

• remove verification-specific client methods from :

• remove obsolete verification model classes:
• update README async methods section and remove verification example

Verification

• Task :compileJava UP-TO-DATE

Task :processResources NO-SOURCE
Task :classes UP-TO-DATE
Task :compileTestJava NO-SOURCE
Task :processTestResources NO-SOURCE
Task :testClasses UP-TO-DATE
Task :test NO-SOURCE

BUILD SUCCESSFUL in 408ms
1 actionable task: 1 up-to-date