abci: remove fee (#2043)

Refs #1861

We don't use the fee field and its likely just confusing.

We can add backwards compatible priority (instead of fee) later.

Note priority is better than fee because it lets the app do the math on how to rank order transactions, rather than forcing that into tendermint (ie. if we return fee, priority would be fee/gas)

docs/app-dev/getting-started.md

@@ -93,9 +93,7 @@ like:
   "jsonrpc": "2.0",
   "id": "",
   "result": {
-    "check_tx": {
-      "fee": {}
-    },
+    "check_tx": {},
     "deliver_tx": {
       "tags": [
         {
@@ -106,8 +104,7 @@ like:
           "key": "YXBwLmtleQ==",
           "value": "YWJjZA=="
         }
-      ],
-      "fee": {}
+      ]
     },
     "hash": "9DF66553F98DE3C26E3C3317A3E4CED54F714E39",
     "height": 14
@@ -219,13 +216,10 @@ the number `1`. If instead, we try to send a `5`, we get an error:
   "jsonrpc": "2.0",
   "id": "",
   "result": {
-    "check_tx": {
-      "fee": {}
-    },
+    "check_tx": {},
     "deliver_tx": {
       "code": 2,
-      "log": "Invalid nonce. Expected 1, got 5",
-      "fee": {}
+      "log": "Invalid nonce. Expected 1, got 5"
     },
     "hash": "33B93DFF98749B0D6996A70F64071347060DC19C",
     "height": 34
@@ -241,12 +235,8 @@ But if we send a `1`, it works again:
   "jsonrpc": "2.0",
   "id": "",
   "result": {
-    "check_tx": {
-      "fee": {}
-    },
-    "deliver_tx": {
-      "fee": {}
-    },
+    "check_tx": {},
+    "deliver_tx": {},
     "hash": "F17854A977F6FA7EEA1BD758E296710B86F72F3D",
     "height": 60
   }