Issue-540: Removed link to UI since only used in downstream product, not OH

[joewxboy]

Pull Request Template

Description

Removed link at the bottom of the installing/many_install.md file that referred to a downstream feature not present in Open Horizon since it resulted in a broken link.

Fixes #540

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

...

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• I have checked my code and corrected any misspellings
• I have tagged the reviewers in a comment below incase my pull request is ready for a review
• I have signed the commit message to agree to Developer Certificate of Origin (DCO) (to certify that you wrote or otherwise have the right to submit your contribution to the project.) by adding "--signoff" to my git commit command.

@open-horizon/documentation-working-group

[euconnor]

Looks good to me