go/{expect,packages/packagestest}: mention the tag+delete proposal

Updates golang/go#70229

Change-Id: I831fe290b8e5ec9d1010e7b9d569543e5c5b2cec
Reviewed-on: https://go-review.googlesource.com/c/tools/+/625921
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: adonovan

go/expect/expect.go

@@ -6,6 +6,10 @@
 Package expect provides support for interpreting structured comments in Go
 source code (including go.mod and go.work files) as test expectations.
 
+[Note: there is an open proposal (golang/go#70229) to deprecate, tag,
+and delete this package. If accepted, the last version of the package
+be available indefinitely but will not receive updates.]
+
 This is primarily intended for writing tests of things that process Go source
 files, although it does not directly depend on the testing package.
 

go/packages/packagestest/export.go

@@ -5,6 +5,10 @@
 /*
 Package packagestest creates temporary projects on disk for testing go tools on.
 
+[Note: there is an open proposal (golang/go#70229) to deprecate, tag,
+and delete this package. If accepted, the last version of the package
+be available indefinitely but will not receive updates.]
+
 By changing the exporter used, you can create projects for multiple build
 systems from the same description, and run the same tests on them in many
 cases.