manifest: use forked art

Change-Id: I4d6f5e9dfee4ed3714d1e40fd93b0d17c9ac5590

omni-aosp.xml

@@ -8,6 +8,7 @@
            fetch="https://github.com/omnirom"
            review="gerrit.omnirom.org" />
 
+  <project path="art" name="android_art" remote="omnirom" revision="android-8.1" groups="pdk" />
   <project path="bionic" name="android_bionic" remote="omnirom" revision="android-8.1" groups="pdk" />
 
   <project path="build/make" name="android_build" remote="omnirom" revision="android-8.1" groups="pdk" >

remove.xml

@@ -8,6 +8,7 @@
   <remove-project name="device/google/wahoo" />
   <remove-project name="device/google/wahoo-kernel" />
 
+  <remove-project name="platform/art" />
   <remove-project name="platform/bionic" />
   <remove-project name="platform/build" />
   <remove-project name="platform/build/soong" />