[dev.typeparams] cmd/compile/internal/types: review of sizes.go

The changes between (equivalent, and reviewed) go/types/sizes.go
and sizes.go can be seen by comparing patchset 1 and 2. The actual
change is just removing the "// UNREVIEWED" marker.

Change-Id: Iacdcffe56023ec53bfaaac8fb112f813a7de0a95
Reviewed-on: https://go-review.googlesource.com/c/go/+/291176


Reviewed-by: Robert Findley <rfindley@google.com>
Trust: Robert Griesemer <gri@golang.org>