all: remove remaining UNREVIEWED files for Unified IR

all: remove remaining UNREVIEWED files for Unified IR

Those ureader.go files have enough documents and in stable
developement/review as other parts of Unified IR.

Fixes #48194

Change-Id: I08a0cbfef05401135b5390e00fe808e838a96170
Reviewed-on: https://go-review.googlesource.com/c/go/+/422617
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>