init: replace Result<> with expected<>

Android-base has an implementation of the future std::expected<>.
This provides the same baseline functionality as Result<>, so use it
instead of our own version.

Bug: 132145659
Test: boot, init unit tests
Change-Id: I11e61bcb5719b262a6420483ed51a762826a9e23
diff --git a/init/reboot.cpp b/init/reboot.cpp
index 0966b6c..54f68bb 100644
--- a/init/reboot.cpp
+++ b/init/reboot.cpp
@@ -527,13 +527,13 @@
 
             // start all animation classes if stopped.
             if (do_shutdown_animation) {
-                service->Start().IgnoreError();
+                service->Start();
             }
             service->SetShutdownCritical();  // will not check animation class separately
         }
 
         if (do_shutdown_animation) {
-            bootAnim->Start().IgnoreError();
+            bootAnim->Start();
             surfaceFlinger->SetShutdownCritical();
             bootAnim->SetShutdownCritical();
         }