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/launcher.aconfig b/aconfig/launcher.aconfig
index c3fb150..06809d7 100644
--- a/aconfig/launcher.aconfig
+++ b/aconfig/launcher.aconfig
@@ -1,5 +1,5 @@
 package: "com.android.launcher3"
-container: "system"
+container: "system_ext"
 
 flag {
     name: "enable_expanding_pause_work_button"