Replace system/update_engine path to new repository android_system_update_engine

Change-Id: I6a3611864b12239b89e04bd6f7d9a98891c08314

omni-aosp.xml

@@ -88,4 +88,5 @@
   <project path="system/sepolicy" name="android_system_sepolicy" remote="omnirom" revision="android-8.1" />
   <project path="system/vold" name="android_system_vold" remote="omnirom" revision="android-8.1" />
   <project path="system/hardware/interfaces" name="android_system_hardware_interfaces" remote="omnirom" revision="android-8.1" />
+  <project path="system/update_engine" name="android_system_update_engine" remote="omnirom" revision="android-8.1" />
 </manifest>

remove.xml

@@ -158,4 +158,5 @@
   <remove-project name="platform/system/sepolicy" />
   <remove-project name="platform/system/vold" />
   <remove-project name="platform/system/hardware/interfaces" />
+  <remove-project name="platform/system/update_engine" />
 </manifest>