ICU-22127 Remove obsolete WordBreakTest.txt known issues

[eggrobin]

Made obsolete by #3249.

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22127
• Required: The PR title must be prefixed with a JIRA Issue number. Example: "ICU-1234 Fix xyz"
• Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• Required: Each commit message must be prefixed with a JIRA Issue number. Example: "ICU-1234 Fix xyz"
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

[jira-pull-request-webhook]

Hooray! The files in the branch are the same across the force-push. 😃

~ Your Friendly Jira-GitHub PR Checker Bot