Remove files/get endpoint which is not used

[gertzakis]

Closes: #N/A

What's Changed

Removes the files/get URL endpoint which is not used. Also, the way it was configured without "add_attachment_headers": True it was missing the Content-Disposition: attachment HTTP header which causes a security vulnerability.

TODO

• Explanation of Change(s)
• Added change log fragment(s) (for more information see the documentation)
• Attached Screenshots, Payload Example
• Unit, Integration Tests
• Documentation Updates (when adding/changing features)
• Example Plugin Updates (when adding/changing features)
• Outline Remaining Work, Constraints from Design

[glennmatthews]

Suggest adding a changes/5109.security change fragment along the lines of:

Removed `/files/get/` URL endpoint (for viewing FileAttachment files in the browser), as it was unused and could potentially pose security issues.

[glennmatthews]

I hadn't noticed that this was a PR to ltm-1.6. This should really go into develop first and then be backported to the LTM branch.

[gertzakis]

Oh of course! Opened #5115 for adding it into develop.