Mark webview2 on winui as non-preview

[captainbrosset]

WinUI was generally released and isn't in preview anymore.
So I'm removing the "preview" note on the webview2 page.

[opbld31]

Docs Build status updates of commit 89ed9c0:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/webview2/index.md	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the docs.microsoft.com contributor guides
• Post your question in the Docs support channel

[jasonstephen15]

Good to merge @Reezaali

[opbld33]

Docs Build status updates of commit e4b3390:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/webview2/index.md	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the docs.microsoft.com contributor guides
• Post your question in the Docs support channel