fix: removed unused PopupHandlerAdapter

[adietish]

depends on

• https://github.com/redhat-developer/intellij-tekton/pull/673
• https://github.com/redhat-developer/intellij-knative/pull/256
• https://github.com/redhat-developer/intellij-kubernetes/pull/769
• https://github.com/redhat-developer/intellij-openshift-connector/pull/872

removed PopupHandlerAdapter since it's not used any more