refactor: use xrpl-codec-gen for definitions.json (#2037)

* Update definitions.json

* update CONTRIBUTING

* fix tests

* fix UNL

CONTRIBUTING.md

@@ -83,6 +83,9 @@ npm run docgen
 
 This updates `docs/` at the top level, where GitHub Pages looks for the docs.
 
+## Update `definitions.json`
+Use [this repo](https://github.com/RichardAH/xrpl-codec-gen) to generate a new `definitions.json` file from the rippled source code. Instructions are available in that README.
+
 ## Adding and removing packages
 
 `xrpl.js` uses `lerna` and `npm`'s workspaces features to manage a monorepo.

packages/ripple-binary-codec/test/fixtures/data-driven-tests.json

@@ -483,13 +483,6 @@
             "type": 5,
             "expected_hex": "5013"
         },
-        {
-            "type_name": "Hash256",
-            "name": "TicketID",
-            "nth_of_type": 20,
-            "type": 5,
-            "expected_hex": "5014"
-        },
         {
             "type_name": "Hash256",
             "name": "Digest",
@@ -721,13 +714,6 @@
             "type": 8,
             "expected_hex": "84"
         },
-        {
-            "type_name": "AccountID",
-            "name": "Target",
-            "nth_of_type": 7,
-            "type": 8,
-            "expected_hex": "87"
-        },
         {
             "type_name": "AccountID",
             "name": "RegularKey",