Remove legacy KM_TAG_CREATION_DATETIME

KM_TAG_CREATION_DATETIME is never set anywhere else and the computation
leads to an unsigned overflow false positive.

Change-Id: I7eca6a975ca2f8b199dfcb4871a1e1d6750afc78
diff --git a/keystore/keystore.cpp b/keystore/keystore.cpp
index 0906abf..21d75be 100644
--- a/keystore/keystore.cpp
+++ b/keystore/keystore.cpp
@@ -256,8 +256,6 @@
     params->push_back(keymaster_param_date(KM_TAG_ORIGINATION_EXPIRE_DATETIME, LLONG_MAX));
     params->push_back(keymaster_param_date(KM_TAG_USAGE_EXPIRE_DATETIME, LLONG_MAX));
     params->push_back(keymaster_param_date(KM_TAG_ACTIVE_DATETIME, 0));
-    uint64_t now = keymaster::java_time(time(NULL));
-    params->push_back(keymaster_param_date(KM_TAG_CREATION_DATETIME, now));
 }
 
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