Stop dropping caches now we have kernel fix

am: 6abe6831b5

Change-Id: Ic87ca15267c205551e0bbfa087ea086d2ebce089

Ext4Crypt.cpp

@@ -171,13 +171,6 @@ static bool install_key(const std::string& key, std::string* raw_ref) {
     LOG(DEBUG) << "Added key " << key_id << " (" << ref << ") to keyring " << device_keyring
                << " in process " << getpid();
 
-    // *TODO* Remove this code when kernel is fixed - see b/28373400
-    // Kernel preserves caches across a key insertion with ext4ice, which leads
-    // to contradictory dirents
-    if (!android::base::WriteStringToFile("3", "/proc/sys/vm/drop_caches")) {
-        PLOG(ERROR) << "Failed to drop_caches";
-    }
-
     return true;
 }