Revert "Update minimum supported targetSdk to 28."

This reverts commit 79185263557759826c41f8f3e1b10629137f2d91.

Reason for revert: <Test break by b/216280809>

Change-Id: I4d11564314034d7596261c1760dd79d3d5b82f2e
diff --git a/core/version_util.mk b/core/version_util.mk
index b835241..b7c4e48 100644
--- a/core/version_util.mk
+++ b/core/version_util.mk
@@ -240,6 +240,6 @@
   # Used to set minimum supported target sdk version. Apps targeting sdk
   # version lower than the set value will result in a warning being shown
   # when any activity from the app is started.
-  PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION := 28
+  PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION := 23
 endif
 .KATI_READONLY := PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION