go/types: don't report errors referring to invalid types or operands

Such errors are likely spurious and caused by previously reported
errors; they don't add valuable information. Simply drop them.

Fixes #24182.

Change-Id: I0ac48c41647c628aa7636b29eaedfd9d01913762
Reviewed-on: https://go-review.googlesource.com/116735


Reviewed-by: Alan Donovan <adonovan@google.com>