common/protob: drop a default field declaration

which triggers nanopb bug https://github.com/nanopb/nanopb/issues/487

common/protob/messages-lisk.proto

@@ -56,7 +56,7 @@ message LiskSignTx {
      */
     message LiskTransactionCommon {
         optional LiskTransactionType type = 1;
-        optional uint64 amount = 2 [default=0];
+        optional uint64 amount = 2;
         optional uint64 fee = 3;
         optional string recipient_id = 4;
         optional bytes sender_public_key = 5;

core/src/trezor/messages/LiskTransactionCommon.py

@@ -41,7 +41,7 @@ class LiskTransactionCommon(p.MessageType):
     def get_fields(cls) -> Dict:
         return {
             1: ('type', p.EnumType("LiskTransactionType", (0, 1, 2, 3, 4, 5, 6, 7)), 0),
-            2: ('amount', p.UVarintType, 0),  # default=0
+            2: ('amount', p.UVarintType, 0),
             3: ('fee', p.UVarintType, 0),
             4: ('recipient_id', p.UnicodeType, 0),
             5: ('sender_public_key', p.BytesType, 0),

python/src/trezorlib/messages/LiskTransactionCommon.py

@@ -41,7 +41,7 @@ class LiskTransactionCommon(p.MessageType):
     def get_fields(cls) -> Dict:
         return {
             1: ('type', p.EnumType("LiskTransactionType", (0, 1, 2, 3, 4, 5, 6, 7)), 0),
-            2: ('amount', p.UVarintType, 0),  # default=0
+            2: ('amount', p.UVarintType, 0),
             3: ('fee', p.UVarintType, 0),
             4: ('recipient_id', p.UnicodeType, 0),
             5: ('sender_public_key', p.BytesType, 0),