omni: remove stock theme overlay

and move pixel to vendor/overlay where it belong

Change-Id: I19bde5b301d821b1e3b8632a00590f0824bab649
diff --git a/config/packages.mk b/config/packages.mk
index b5980bc..432143b 100644
--- a/config/packages.mk
+++ b/config/packages.mk
@@ -45,8 +45,7 @@
 
 # Themes
 PRODUCT_PACKAGES += \
-    PixelTheme \
-    Stock
+    PixelTheme
 
 # for fun
 PRODUCT_PACKAGES += EggGame