remove rewards from the available balance

The rationale is to have an easy way to show what's the spendable UTxO amount.

lib/core-integration/src/Test/Integration/Scenario/API/Shelley/StakePools.hs

@@ -164,11 +164,7 @@ spec = do
             verify r
                 [ expectField (#balance . #getApiT . #reward) (.> (Quantity 0))
                 ]
-            let Quantity totalBalance =
-                    getFromResponse (#balance . #getApiT . #total) r
-            let Quantity rewardBalance =
-                    getFromResponse (#balance . #getApiT . #reward) r
-            pure $ Quantity (totalBalance - rewardBalance)
+            pure $ getFromResponse (#balance . #getApiT . #available) r
 
         -- Use rewards
         addrs <- listAddresses @n ctx w

lib/core/src/Cardano/Wallet/Api/Server.hs

@@ -613,7 +613,7 @@ mkShelleyWallet ctx wid cp meta pending progress = do
     pure ApiWallet
         { addressPoolGap = ApiT $ getState cp ^. #externalPool . #gap
         , balance = ApiT $ WalletBalance
-            { available = Quantity $ reward + availableBalance pending cp
+            { available = Quantity $ availableBalance pending cp
             , total = Quantity $ reward + totalBalance pending cp
             , reward = Quantity reward
             }

specifications/api/swagger.yaml

@@ -341,13 +341,13 @@ x-walletBalance: &walletBalance
   properties:
     available:
       <<: *amount
-      description: Available balance (funds that can be spent)
+      description: Available UTxO balance (funds that can be spent without condition).
     reward:
       <<: *amount
       description: The balance of the reward account for this wallet.
     total:
       <<: *amount
-      description: Total balance (available balance plus pending change)
+      description: Total balance (available balance plus pending change and reward balance).
 
 x-byronWalletBalance: &byronWalletBalance
   description: Byron wallet's current balance(s)