go/types: remove unused return value

Port of https://go-review.googlesource.com/10773 from x/tools.

Change-Id: I6aba6a63a5448b8fcbcc7f072c627c27965dbe20
Reviewed-on: https://go-review.googlesource.com/10774Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/types/typexpr.go

@@ -140,8 +140,8 @@ func (check *Checker) typ(e ast.Expr) Type {
 	return check.typExpr(e, nil, nil)
 }
 
-// funcType type-checks a function or method type and returns its signature.
-func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast.FuncType) *Signature {
+// funcType type-checks a function or method type.
+func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast.FuncType) {
 	scope := NewScope(check.scope, "function")
 	check.recordScope(ftyp, scope)
 
@@ -202,8 +202,6 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast
 	sig.params = NewTuple(params...)
 	sig.results = NewTuple(results...)
 	sig.variadic = variadic
-
-	return sig
 }
 
 // typExprInternal drives type checking of types.