Commit 0e6a6c51 removed readyExecute a long time ago, but left behind
the g.readyg field that was used by readyExecute. Remove this now
unused field.

Change-Id: I41b87ad2b427974d256ec7a7f6d4bdc2ce8a13bb
Reviewed-on: https://go-review.googlesource.com/13111Reviewed-by: Rick Hudson <rlh@golang.org>