Remove redirect to index after settings update

[M-Lipin]

Fixes #15678

The reason of the issue is that updating database and cache may be performed little later the page is fetched on redirection after postback. The se old values may be shown to the user after saving the settings.

It seems that we don't need to redirect after saving because the data maybe actual and up-to-date with straightforward page life cycle without redirect.

[sebastienros]

I believe we should keep a redirect after POSTs or refreshing the pages will do a re-submission.
The problem is probably a caching issue, and the Index action should re-load the information to display.

[MikeAlhayek]

It would have to be caching. And I am thinking the second request is being handled by a different server. Because if this was handled by the same server, then the server would render the updated values.

@M-Lipin is your application running on a single web server instance or is your app being scaled to multiple instances? If it is multiple instances, is your environment setup to keep the client one a single web instance or does it assign the user to any available web service instance per request? In other words, is the ARR Affinity cookie is enabled?

[MikeAlhayek]

@M-Lipin we are going to be undoing this PR. Can you please provide your input on the last comment above?