remove unneeded crypto code

Author: nplasterer

library/src/main/java/org/xmtp/android/library/Crypto.kt

@@ -98,19 +98,5 @@ class Crypto {
             hkdfGenerator.generateBytes(hkdf, 0, hkdf.size)
             return hkdf
         }
-
-        fun generateHmacSignature(
-            secret: ByteArray,
-            info: ByteArray,
-            message: ByteArray,
-        ): ByteArray {
-            val derivationParameters = HKDFParameters(secret, ByteArray(0), info)
-            val digest = SHA256Digest()
-            val hkdfGenerator = HKDFBytesGenerator(digest)
-            hkdfGenerator.init(derivationParameters)
-            val hkdf = ByteArray(32)
-            hkdfGenerator.generateBytes(hkdf, 0, hkdf.size)
-            return calculateMac(hkdf, message)
-        }
     }
 }

library/src/main/java/org/xmtp/android/library/messages/MessageV2.kt

@@ -156,7 +156,10 @@ class MessageV2Builder(val senderHmac: ByteArray? = null, val shouldPush: Boolea
             val info = "$thirtyDayPeriodsSinceEpoch-${client.address}"
             val infoEncoded = info.toByteStringUtf8().toByteArray()
             val senderHmacGenerated =
-                Crypto.generateHmacSignature(keyMaterial, infoEncoded, headerBytes)
+                Crypto.calculateMac(
+                    Crypto.deriveKey(keyMaterial, ByteArray(0), infoEncoded),
+                    headerBytes
+                )
 
             return buildFromCipherText(
                 headerBytes,