Test strikethrough fix in Aztec

[cameronvoell]

Fixes #wordpress-mobile/gutenberg-mobile#729

To test:

1. Create a new post
2. Press strikethrough button
3. Start typing
4. add some none strikethrough text afterwards or navigate to a new block
5. Return to strikethrough text and verify the strikethrough toolbar button is highlighted
6. highlight the strikethrough text
7. press the strikethrough button
8. verify that the text is no longer showing strikethrough

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[cameronvoell]

Branches need to be rebaseed because of gutenberg changes that only landed in gutenberg/after_release_1.33.0. Will update tomorrow.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APK here.