nem: Remove NEM_DECRYPTED_PAYLOAD_SIZE

It is broken and completely useless

nem.h

@@ -56,7 +56,6 @@
 #define NEM_ENCRYPTED_PAYLOAD_SIZE(size) (AES_BLOCK_SIZE + NEM_SALT_SIZE + NEM_ENCRYPTED_SIZE(size))
 
 #define NEM_DECRYPTED_SIZE(buffer, size)         ((size) - ((buffer)[(size) - 1]))
-#define NEM_DECRYPTED_PAYLOAD_SIZE(buffer, size) NEM_DECRYPTED_SIZE((buffer), (size) - AES_BLOCK_SIZE - NEM_SALT_SIZE)
 
 typedef struct {
 	ed25519_public_key public_key;