x/tools/gopls: redundant diagnostics due to quick fixes

[findleyr]

The following code causes three "too many returns" diagnostics in gopls. Notably, the present but empty result list is required, so this is probably a low priority bug.

func _() () {
  return 0
}

It looks like somehow the "fillreturns" and "noresultvalues" analyzers are colliding, and causing duplication. This may manifest in other ways as we add more quick fixes.

[gopherbot]

Change https://go.dev/cl/650217 mentions this issue: gopls/internal/analysis: simplify type-error analyzers with Cursor