go: Roll Goopfile, remove two no longer used packages.

go/README.md

 # Chromium Infra Go Area
 
 [TOC]
 
 ## Why Go?
 
 Python is great, except when you need to deploy same python program (with tons
 of dependencies) simultaneously to Windows, Mac and Linux machines, or when
 "lets fetch all the source code and just run it" approach no longer works.
 
@@ skipping 145 matching lines @@
     vi Goopfile
     ./env.py goop update
     git diff Goopfile.lock
 
     # Rinse and repeat until all Win dependencies added.
     git add ...
     git commit --amend
     git cl upload
     git cl try -m tryserver.infra -b "Infra Win Tester"
 
+If you suspect that some packages are no longer needed, you can run
+clean_goop.py script. It will detect potentially unused packages and print them.
+It's not fully trusted to work yet, and thus it's not used automatically.
+
+    ./env.py python clean_goop.py
+    <remove what it said to remove>
+
+    ./env.py goop update
+    git diff Goopfile.lock
+    <ensure packages are gone from Goopfile.lock>
+
+    # Test that our code still works.
+    ./env.py go test github.com/luci/gae/...
+    ./env.py go test github.com/luci/luci-go/...
+    ./env.py go test infra/...
+
+Note: both roll_goop.py and clean_goop.py have lists of exceptional packages
+hardcoded in them. If you encounter some stubborn package that is handled badly
+by these scripts, consider adding it to the exceptions.
+
 
 ## Git mirrors for dependencies
 
 All dependencies should be fetched from a *.googlesource.com host.
 
 Some Golang related packages are already on *.googlesource.com (though it may
 be non obvious at the first glance). For example all golang.org/x/* ones are
 actually served from https://go.googlesource.com/.
 
 If you are positive that mirror is needed, file
 [Infra-Git](https://code.google.com/p/chromium/issues/entry?template=Infra-Git)
 ticket specifying what repository you need to be mirrored.