[flutter_markdown] Remove ignored file (#351)
[flutter_markdown] Remove ignored file (#351)

Fixes a new publish warning by removing a file that should be ignored,
but was checked in.

Part of https://github.com/flutter/flutter/issues/82368
flutter/packages,flutter/packages,flutter/packages,flutter/packages,flutter/packages,flutter/packages,flutter/packages,flutter/packages,flutter/packages,flutter/packages