chat: RIP modules, long live gosh+v23test

Also, per discussion:
- Moves 'v23test' package to x/ref/test/v23test
- Makes 'expect' package explicitly depend on 'testing', now
that 'modules' doesn't pass it an interface

MultiPart: 5/7

Change-Id: Idd9624eacb0ddc2d73c6ae5716ec0cf29b241ce6
diff --git a/clients/shell/go/src/v.io/x/chat/channel_test.go b/clients/shell/go/src/v.io/x/chat/channel_test.go
index 2d5d4dc..4c233a5 100644
--- a/clients/shell/go/src/v.io/x/chat/channel_test.go
+++ b/clients/shell/go/src/v.io/x/chat/channel_test.go
@@ -14,8 +14,8 @@
 	"v.io/v23/options"
 	"v.io/x/lib/gosh"
 	"v.io/x/ref/lib/signals"
-	"v.io/x/ref/lib/v23test"
 	"v.io/x/ref/services/mounttable/mounttablelib"
+	"v.io/x/ref/test/v23test"
 )
 
 // TODO(sadovsky): Switch to using v23test.Shell.StartRootMountTable.