twitter adapter: doubled button for a tweet after theme change

[dimasg]

Reproduced with exercise 12, dark theme support.

1. Build and run excersise, configure and enable in extension
2. Open some tweet, for example https://twitter.com/github/status/1521896072037249027
3. Switch theme via left menu

Expecting behaviour:
Theme switched, one button according the theme color

Current result:
Theme switched, two buttons according the theme color.