Remove duplicate nested CSS in ChatMessage.tsx

[Simarjeet112]

This PR removes a duplicate nested &.local CSS block in ChatMessage.tsx (lines 78–85).

Impact:

• No functional change
• Removes dead/duplicate CSS
• Improves maintainability

Tested locally:

• Verified chat message styling
• Verified private message styling
• No UI regression observed

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[Simarjeet112]

I have signed the individual CLA. Thank you.