Remove menu options for disabled features

[bruno-atmire]

References

Fixes #1125
Fixes #1019 (by removing disabled features)
Fixes #1155 (by removing disabled features)

Description

• Removed duplicate curation_tasks menu item because it would be overridden by this item anyway.
• Commented out all menu items that currently don't have a link defined.

Instructions for Reviewers

Log into DSpace and verify that all disabled menu items are gone from the sidebar.

Checklist

• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes TSLint validation using yarn run lint
• My PR doesn't introduce circular dependencies
• My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• If my PR includes new, third-party dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.

[tdonohue]

👍 Looks good to me, thanks @bruno-atmire ! I gave it a quick test and it works as expected...no more disabled features are shown in the sidebar.