go/types: move MethodSetCache into package go/types/typeutil

Change-Id: Iba5d7c2df533948a5b28373b077cc0476a6745ad
Reviewed-on: https://go-review.googlesource.com/10770
Reviewed-by: Alan Donovan <adonovan@google.com>
diff --git a/go/ssa/ssa.go b/go/ssa/ssa.go
index 01ee46a..f4c64bb 100644
--- a/go/ssa/ssa.go
+++ b/go/ssa/ssa.go
@@ -24,7 +24,7 @@
 	imported   map[string]*Package         // all importable Packages, keyed by import path
 	packages   map[*types.Package]*Package // all loaded Packages, keyed by object
 	mode       BuilderMode                 // set of mode bits for SSA construction
-	MethodSets types.MethodSetCache        // cache of type-checker's method-sets
+	MethodSets typeutil.MethodSetCache     // cache of type-checker's method-sets
 
 	methodsMu    sync.Mutex                 // guards the following maps:
 	methodSets   typeutil.Map               // maps type to its concrete methodSet