omni: PreferenceTheme does not need system_current sdk

Change-Id: I037421e217c2091edf7a2add07bf1613560fde58
diff --git a/themes/PreferenceTheme/Android.bp b/themes/PreferenceTheme/Android.bp
index 90fd482..261947d 100644
--- a/themes/PreferenceTheme/Android.bp
+++ b/themes/PreferenceTheme/Android.bp
@@ -8,6 +8,6 @@
         "com.google.android.material_material",
     ],
 
-    sdk_version: "system_current",
+    sdk_version: "current",
     min_sdk_version: "31",
 }