remove unused arg

README.rst

@@ -108,14 +108,13 @@ Methods
 
 * Returns: ``bytes``
 
-``ecdh(public_key, update=False)``
+``ecdh(public_key)``
 
 Computes a Diffie-Hellman secret in constant time.
 
 * Parameters:
 
     - **public_key** (``bytes``) - Another party's public key in compressed or uncompressed form.
-    - **update** - If ``True``, will update and return ``self``.
 
 * Returns: ``bytes``
 

coincurve/keys.py

@@ -58,7 +58,7 @@ class PrivateKey:
 
         return recoverable_to_der(signature, self.context)
 
-    def ecdh(self, public_key, update=False):
+    def ecdh(self, public_key):
         secret = ffi.new('unsigned char [32]')
 
         lib.secp256k1_ecdh(