Update git submodules

* Update system/core from branch 'master'
  to 6ecedd2040d0b8260b83e5d2af99e9db703a7fb6
  - Merge "libsnapshot: Track the source slot across reboots."
  - libsnapshot: Track the source slot across reboots.
    
    The purpose of this is twofold. First, we need a way to detect whether
    the device has booted into the new slot after an update. Second, we need
    a quick-and-dirty test for first-stage init so it can avoid searching
    for snapshots if it doesn't need to.
    
    We can solve both of these problems by storing the source slot in
    /metadata/ota/snapshot-boot. The existence of the file implies a more
    complex check is needed, and the file stores the source slot.
    
    Test: libsnapshot_test gtest
    Bug: 139204329
    Bug: 139089801
    Change-Id: I919dd1c27a65734c61f3a9bdffefb32bdebd723b
    
diff --git a/system/core b/system/core
index 93619e3..6ecedd2 160000
--- a/system/core
+++ b/system/core
@@ -1 +1 @@
-Subproject commit 93619e373a60c967623e064f9aa5424d4b38e8e2
+Subproject commit 6ecedd2040d0b8260b83e5d2af99e9db703a7fb6