Remove enterprise dashboard improvements toggle

[jingcheng16]

Product Description

Technical Summary

Ticket: https://dimagi.atlassian.net/browse/SAAS-16377
We hide Security Center page when this page doesn't have any tile.
Since Two Factor Authentication Tile is now developed, we should remove the toggle to release the page and the tile.

Feature Flag

Safety Assurance

Safety story

Verified locally and on staging

Automated test coverage

QA Plan

Rollback instructions

• This PR can be reverted after deploy with no further considerations

Labels & Review

• Risk label is set correctly
• The set of people pinged as reviewers is appropriate for the level of risk of the change

[sentry-io]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: corehq/tabs/tabclasses.py

Function	Unhandled Issue
sidebar_items	NameError: name 'ConnectMesssagingUserView' is not defined /a/{domain}/messaging/... Event Count: 28
sidebar_items	NameError: name 'ConnectMesssagingUserView' is not defined /a/{domain}/messaging/co... Event Count: 5
sidebar_items	NameError: name 'ConnectMesssagingUserView' is not defined /a/{domain}/messaging/b... Event Count: 1

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