Kibana shouldn't display warnings which give access to advanced settings in iFrames

[bhavyarm]

Kibana version: 7.15.0 bc

Elasticsearch version: 7.15.0 bc

Server OS version: darwin_x86_64

Browser version: chrome latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): from staging

Describe the bug: Kibana shouldn't display warnings that give access to advanced settings in iFrames. Because once you kick on iFrames having access means you can click on everything else.

Steps to reproduce:

1. Turn on legacy chart switch in advanced settings - visualization:visualize:legacyChartsLibrary and go to visualize and create a chart
2. Click on share and share the viz as an iFrame - create html file with that code
3. Open the iFrame (do it in firefox so you don't have to set additional settings in kibana.yml)
4. You see the warning about legacy viz and how to change it in advanced settings
5. You can click on the advanced setting and boom you can be all over Kibana if you have access

Expected behavior: Don't display warnings in iFrames

Screenshots (if relevant):

access_iFrame.mp4

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[nreese]

Closing, legacy charts library has been removed