Revert "Replace system_ext container with system"

This reverts commit d80efafdc0df5afae43883778202c243e21b0e45.

A system partition cannot have the aconfigs of other partitions.
Revive the system_ext container for system_ext aconfigs.

Bug: 385213580
Test: "adb shell aflags list" must not be changed.
Flag: EXEMPT refactor
Change-Id: I92387e6d5764c750f83bd8d266f6da969e114a72
diff --git a/aconfig/Android.bp b/aconfig/Android.bp
index 5413601..bca7494 100644
--- a/aconfig/Android.bp
+++ b/aconfig/Android.bp
@@ -20,7 +20,7 @@
 aconfig_declarations {
     name: "com_android_launcher3_flags",
     package: "com.android.launcher3",
-    container: "system",
+    container: "system_ext",
     srcs: ["**/*.aconfig"],
 }