Revert "update_engine: Support milestones to EOL from Omaha"

This reverts commit 893cae4b0e5141bcaf9f56b1775e681c8f523630.

Reason for revert: use of EOL date and EOL notification date instead milestones to EOL.

Original change's description:
> update_engine: Support milestones to EOL from Omaha
>
> Initiative to show EOL message on Chrome OS devices require that
> update_engine parses the fields within Omaha response that pertain to the
> new milestones to EOL field. The Omaha response will include a new
> field called "milestones_to_eol" which will be an integer value
> string.
>
> The job of update_engine when it comes to milestones to EOL from Omaha
> is to merely forward. No checks and no modifications of fields are
> done within update_engine besides being able to convert the milestones
> to EOL from a string to integer.
>
> BUG=chromium:994999
> TEST=FEATURES="test" emerge-$BOARD update_engine update_engine-client
> TEST=cros deploy $IP update_engine update_engine-client
> TEST=test_that -b $BOARD $IP autoupdate_EOL # from Cq-Depend
> TEST=test_that -b $BOARD $IP autoupdate_EOL.milestones # from Cq-Depend
>
> Cq-Depend:chromium:1761371
> Change-Id: I268e4c8e641b17d6a727a50f53285cc97c76eb22
> Reviewed-on: https://chromium-review.googlesource.com/1759285
> Tested-by: Jae Hoon Kim <kimjae@chromium.org>
> Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
> Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
> Reviewed-by: Nicolas Norvez <norvez@chromium.org>
> Reviewed-by: Amin Hassani <ahassani@chromium.org>

TBR=maybelle@chromium.org,norvez@chromium.org,ahassani@chromium.org,abutzier@chromium.org,chromiumos-cl-exonerator@appspot.gserviceaccount.com,kimjae@chromium.org

BUG=chromium:994999
TEST=none
Cq-Depend:chromium:1782971
Change-Id: I42e75e22948b3653500d355027dc3312015c9ebf
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/1782970
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/omaha_request_action.h b/omaha_request_action.h
index 0c256a8..8dffb5c 100644
--- a/omaha_request_action.h
+++ b/omaha_request_action.h
@@ -144,7 +144,6 @@
               GetInstallDateWhenOOBECompletedWithValidDate);
   FRIEND_TEST(OmahaRequestActionTest,
               GetInstallDateWhenOOBECompletedDateChanges);
-  FRIEND_TEST(OmahaRequestActionTest, PersistEolStatusTest);
   friend class UpdateAttempterTest;
   FRIEND_TEST(UpdateAttempterTest, SessionIdTestEnforceEmptyStrPingOmaha);
   FRIEND_TEST(UpdateAttempterTest, SessionIdTestConsistencyInUpdateFlow);
@@ -189,9 +188,8 @@
   bool PersistCohortData(const std::string& prefs_key,
                          const std::string& new_value);
 
-  // Parse and persist the end-of-life status flag and milestones to EOL sent
-  // back in the updatecheck tag attributes. The flag will be validated and
-  // stored in the Prefs.
+  // Parse and persist the end-of-life status flag sent back in the updatecheck
+  // tag attributes. The flag will be validated and stored in the Prefs.
   bool PersistEolStatus(const std::map<std::string, std::string>& attrs);
 
   // If this is an update check request, initializes