Revert "Add return_op to finalizeOp"

This reverts commit 2c55d92.

This approach doesn't work because calling sync method of superclass via
`super()` still uses async `AbstractGrapheneChain` (instantiated
`self.blockchain.finalizeOp` which is coroutine and needed to be called with
`await`).

graphenecommon/chain.py

@@ -157,7 +157,7 @@ def set_shared_config(self, config):
     # -------------------------------------------------------------------------
     # General transaction/operation stuff
     # -------------------------------------------------------------------------
-    def finalizeOp(self, ops, account, permission, return_op=False, **kwargs):
+    def finalizeOp(self, ops, account, permission, **kwargs):
         """ This method obtains the required private keys if present in
             the wallet, finalizes the transaction, signs it and
             broadacasts it
@@ -172,8 +172,6 @@ def finalizeOp(self, ops, account, permission, return_op=False, **kwargs):
                 ProposalsBuilder (see :func:`new_proposal`) or
                 TransactionBuilder (see :func:`new_tx()`) to specify
                 where to put a specific operation.
-            :param bool return_op: Instead of finalizing transaction, simply
-                return ops as is
 
             ... note:: ``append_to`` is exposed to every method used in the
                 this class
@@ -190,9 +188,6 @@ def finalizeOp(self, ops, account, permission, return_op=False, **kwargs):
                 :class:`transactionbuilder.TransactionBuilder`.
                 You may want to use your own txbuffer
         """
-        if return_op:
-            return ops
-
         if "append_to" in kwargs and kwargs["append_to"]:
             if self.proposer:
                 log.warning(