CI_Encryption: Remove ARCFour from aliased ciphers due ...

Seems like there are some issues with it
diff --git a/system/libraries/Encryption.php b/system/libraries/Encryption.php
index 2d3f82d..503fb64 100644
--- a/system/libraries/Encryption.php
+++ b/system/libraries/Encryption.php
@@ -718,13 +718,11 @@
 					'aes-128' => 'rijndael-128',
 					'aes-192' => 'rijndael-128',
 					'aes-256' => 'rijndael-128',
-					'des3-ede3' => 'tripledes',
-					'rc4-40' => 'arcfour'
+					'des3-ede3' => 'tripledes'
 				),
 				'openssl' => array(
 					'rijndael-128' => 'aes-128',
-					'tripledes' => 'des-ede3',
-					'arcfour' => 'rc4-40'
+					'tripledes' => 'des-ede3'
 				)
 			);