tracing: Set user_events to BROKEN

After being merged, user_events become more visible to a wider audience
that have concerns with the current API. It is too late to fix this for
this release, but instead of a full revert, just mark it as BROKEN (which
prevents it from being selected in make config). Then we can work finding
a better API. If that fails, then it will need to be completely reverted.

Link: https://lore.kernel.org/all/2059213643.196683.1648499088753.JavaMail.zimbra@efficios.com/
Link: https://lkml.kernel.org/r/20220330155835.5e1f6669@gandalf.local.home



Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>