libartpalette: Fix non-existent required dependency

HOST_CROSS module host_cross_libartpalette has non-existent required: host_cross_libartpalette-system
HOST_CROSS module host_cross_libartpalette_64 has non-existent required: host_cross_libartpalette-system

Only specify required dependency for device variant because only device
variant is dlopen()-ing libartpalette-system.so

Bug: 7456955
Test: TH presubmit
Test: m com.android.art.debug # libartpalette-system is also installed
Change-Id: I04aac73ba769d78ebb774ec5a6c243628e23d70f
diff --git a/libartpalette/Android.bp b/libartpalette/Android.bp
index 3f076d1..1ccc5e4 100644
--- a/libartpalette/Android.bp
+++ b/libartpalette/Android.bp
@@ -40,12 +40,13 @@
 art_cc_library {
     name: "libartpalette",
     defaults: ["libartpalette_defaults"],
-    required: ["libartpalette-system"], // libartpalette.so dlopen()'s libartpalette-system.
     header_libs: ["libbase_headers"],
     target: {
         // Targets supporting dlopen build the client library which loads
         // and binds the methods in the libartpalette-system library.
         android: {
+            // libartpalette.so dlopen()'s libartpalette-system.
+            required: ["libartpalette-system"],
             srcs: ["apex/palette.cc"],
             shared_libs: ["liblog"],
             version_script: "libartpalette.map.txt",