`Development`: Remove experimental and beta tag

[minrows]

Checklist

• [x] I added multiple screenshots/screencasts of my UI changes

Motivation and Context

This PR removes the experimental tag from the theme switcher popup and the beta tag from Flowchart.

Steps for Testing

Test Server

• Goto test server
• Click on File >New from the menu
• Observe that the beta tag is removed from Flowchart
• Hover on theme switcher icon
• Observe that the Experimental tag is removed from the popup

Screenshots

Before

After

[stefanwaldhauser]

I approve this change :)

[simon-hng]

looks good