Remove HTML tags from error message when creating user in multisite
Before, error message is like this:
Error: <strong>Error:</strong> This email address is already registered. <a href="http://bahu.local/wp-login.php">Log in</a> with this address or choose another one.
After:
Error: This email address is already registered. Log in with this address or choose another one.
Fixes https://github.com/wp-cli/entity-command/issues/472
Before, error message is like this:
After: