Remove FIXME for missing fields

Investigate and remove the fixme, leave a more terse comment incase
someone stumbles upon this later.

Author: tcharding

json/src/v17/wallet.rs

@@ -167,13 +167,8 @@ pub struct GetTransaction {
     pub amount: f64,
     pub fee: Option<f64>,
     pub confirmations: u32,
-    // FIXME: The docs say these two fields should be here but it is not returned.
-    //        Is it worth patching Core for a version this old?
-    //
-    // #[serde(rename = "blockhash")]
-    // pub block_hash: String,
-    // #[serde(rename = "blockindex")]
-    // pub block_index: u64,
+    // The docs say there should be two more fields: `blockhash` and `blockindex` but integration
+    // test fails if we add them i.e., they are not returned by `v0.17.1`.
     pub txid: String,
     pub time: u64,
     #[serde(rename = "timereceived")]