go/types, types2: remove superfluous unalias call (minor cleanup)

Change-Id: Ifc0d6e999777513498f070c5bc2fb4640d38c671
Reviewed-on: https://go-review.googlesource.com/c/go/+/712460
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Mark Freeman <markfreeman@google.com>

Author: Robert Griesemer

src/cmd/compile/internal/types2/alias.go

@@ -113,7 +113,6 @@ func unalias(a0 *Alias) Type {
 	for a := a0; a != nil; a, _ = t.(*Alias) {
 		t = a.fromRHS
 	}
-
 	// It's fine to memoize nil types since it's the zero value for actual.
 	// It accomplishes nothing.
 	a0.actual = t

src/cmd/compile/internal/types2/signature.go

@@ -203,7 +203,7 @@ func (check *Checker) collectRecv(rparam *syntax.Field, scopePos syntax.Pos) (*V
 			case *Alias:
 				// Methods on generic aliases are not permitted.
 				// Only report an error if the alias type is valid.
-				if isValid(unalias(t)) {
+				if isValid(t) {
 					check.errorf(rbase, InvalidRecv, "cannot define new methods on generic alias type %s", t)
 				}
 				// Ok to continue but do not set basetype in this case so that

src/go/types/alias.go

@@ -226,7 +226,7 @@ func (check *Checker) collectRecv(rparam *ast.Field, scopePos token.Pos) (*Var,
 			case *Alias:
 				// Methods on generic aliases are not permitted.
 				// Only report an error if the alias type is valid.
-				if isValid(unalias(t)) {
+				if isValid(t) {
 					check.errorf(rbase, InvalidRecv, "cannot define new methods on generic alias type %s", t)
 				}
 				// Ok to continue but do not set basetype in this case so that