Always powerwash on channel change if arbitrary channel allowed.

Merged is_powerwash_allowed() and to_more_stable_channel() into
ShouldPowerwash().

Bug: 73082835
Test: update_engine_unittests
Change-Id: I6b7af0d1dac28d5fa9cddf4391bbd9cdf2acb57b
diff --git a/omaha_request_action_unittest.cc b/omaha_request_action_unittest.cc
index 87dc404..2f466dd 100644
--- a/omaha_request_action_unittest.cc
+++ b/omaha_request_action_unittest.cc
@@ -2188,8 +2188,7 @@
   params.set_current_channel("canary-channel");
   EXPECT_TRUE(params.SetTargetChannel("stable-channel", true, nullptr));
   params.UpdateDownloadChannel();
-  EXPECT_TRUE(params.to_more_stable_channel());
-  EXPECT_TRUE(params.is_powerwash_allowed());
+  EXPECT_TRUE(params.ShouldPowerwash());
   ASSERT_FALSE(TestUpdateCheck(&params,
                                "invalid xml>",
                                -1,
@@ -2223,8 +2222,7 @@
   params.set_current_channel("stable-channel");
   EXPECT_TRUE(params.SetTargetChannel("canary-channel", false, nullptr));
   params.UpdateDownloadChannel();
-  EXPECT_FALSE(params.to_more_stable_channel());
-  EXPECT_FALSE(params.is_powerwash_allowed());
+  EXPECT_FALSE(params.ShouldPowerwash());
   ASSERT_FALSE(TestUpdateCheck(&params,
                                "invalid xml>",
                                -1,