Update `cy.axeFlush()` to `cy.axeWatcherFlush()` in all cypress tests

[dequejenn]

We are deprecating cy.axeFlush() and that needs to be reflected in the Cypress examples:

• [ ] https://github.com/dequelabs/watcher-examples/blob/a54beef0d65d0bc8a1656d1f349725037e955f49/cypress/basic/cypress/support/e2e.js#L6
• [ ] https://github.com/dequelabs/watcher-examples/blob/a54beef0d65d0bc8a1656d1f349725037e955f49/cypress/iframes/cypress/support/e2e.js#L6
• [ ] https://github.com/dequelabs/watcher-examples/blob/a54beef0d65d0bc8a1656d1f349725037e955f49/cypress/manual-mode/cypress/support/e2e.js#L6
• [ ] https://github.com/dequelabs/watcher-examples/blob/a54beef0d65d0bc8a1656d1f349725037e955f49/cypress/multi-page/cypress/support/e2e.js#L6

[davidg-dq]

Looks like @Zidious took care of this last month.