Portfolio Objective option cannot be hidden for existing Themes.

Issue Summary

"Theme" field can be hidden in the "Create New Objective" for the Portfolio tier window
but the Objective option cannot be hidden for existing Themes.
Expectation is that there should be an option to hide the Objectives from the Portfolio Tier Window. All the other fields in the Portfolio Tier window can be hidden in the Theme Details Panel, however Objectives cannot.
Quote:
"This is inconsistent.
Prevents ensuring systematically that Themes are:
1. Only assigned to Enterprise-level Strategic Objectives, and
2. Never assigned to Portfolio-level Portfolio Objectives."

Steps to Reproduce

1. Administration | Settings | Details Panels Settings
2. In the Work Item dropdown box, select "Theme"

Expected Results

There is an option to hide Objectives.

Actual Results

There is no option to hide Objectives.

Workaround

There is a workaround if you want end users to not add Objectives in this panel.
Administration | Roles |_choose the role _|Portfolio | Manage | Portfolio Objectives
Toggle "Portfolio Objectives" off