x/tools/gopls: unhandled named anchor on the hover

[hyangah]

Either we need to drop or translate to a reasonable markdown element.

[gopherbot]

Change https://go.dev/cl/456535 mentions this issue: gopls/hover: remove header tags from hover markdown

[gopherbot]

Change https://go.dev/cl/456641 mentions this issue: gopls/hover: remove header tags from hover markdown