Revert "Update Security String to 2021-10-06"

This reverts commit 61275cd338876579ddbaa9b1cd0278c45138c003.

Reason for revert: SPL bump no longer necessary due to ATT FRC respin

Bug: 193547118
Change-Id: I1df0e12d50471b518653ff865637193bd7ed9101
(cherry picked from commit 1f04c4d3e7af6566b7d284d2db4953b7ad151571)
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index d549602..85f63c9 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -240,7 +240,7 @@
     #  It must be of the form "YYYY-MM-DD" on production devices.
     #  It must match one of the Android Security Patch Level strings of the Public Security Bulletins.
     #  If there is no $PLATFORM_SECURITY_PATCH set, keep it empty.
-      PLATFORM_SECURITY_PATCH := 2021-10-06
+      PLATFORM_SECURITY_PATCH := 2021-10-05
 endif
 .KATI_READONLY := PLATFORM_SECURITY_PATCH