APIv2(DeliverMax): add alias for Amount in Payment transactions (#4733)

Using the "Amount" field in Payment transactions can cause incorrect
interpretation. There continue to be problems from the use of this
field. "Amount" is rarely the correct field to use; instead,
"delivered_amount" (or "DeliveredAmount") should be used.

Rename the "Amount" field to "DeliverMax", a less misleading name. With
api_version: 2, remove the "Amount" field from Payment transactions.

- Input: "DeliverMax" in `tx_json` is an alias for "Amount"
  - sign
  - submit (in sign-and-submit mode)
  - submit_multisigned
  - sign_for
- Output: Add "DeliverMax" where transactions are provided by the API
  - ledger
  - tx
  - tx_history
  - account_tx
  - transaction_entry
  - subscribe (transactions stream)
- Output: Remove "Amount" from API version 2

Fix #3484

Fix #3902

Builds/levelization/results/ordering.txt

@@ -130,6 +130,7 @@ test.csf > ripple.json
 test.csf > ripple.protocol
 test.json > ripple.beast
 test.json > ripple.json
+test.json > ripple.rpc
 test.json > test.jtx
 test.jtx > ripple.app
 test.jtx > ripple.basics