Surface removed LCP element in report

**Summary**
Most of this discussion is happening in chat, but filing an issue so we don't forget. ref https://github.com/GoogleChrome/lighthouse/pull/11625#issuecomment-721857525

LCP changed in m88 to now include removed elements. When this happens and there's a GC we can't find the LCP element anymore and the audit gets marked as not applicable. At that time we may also optionally consider removing `_maxChromiumMilestone` support from smoke tests.