credstore: remove unused variable

Test: mmm system/security
Change-Id: I50f80bd823c9039eaa05cc724077f297af550462
diff --git a/identity/CredentialData.cpp b/identity/CredentialData.cpp
index 803e671..ecf2258 100644
--- a/identity/CredentialData.cpp
+++ b/identity/CredentialData.cpp
@@ -527,7 +527,6 @@
         return nullptr;
     }
 
-    int n = 0;
     for (AuthKeyData& data : authKeyDatas_) {
         if (nowMilliSeconds > data.expirationDateMillisSinceEpoch) {
             if (!allowUsingExpiredKeys) {
@@ -540,7 +539,6 @@
                 candidate = &data;
             }
         }
-        n++;
     }
 
     if (candidate == nullptr) {