Lower cost of joining and quitting in STAKE_POOLS_{JOIN,QUIT}_01x.

A previous commit adjusted the dummy output used by function
`performSelectionEmpty` so that it uses a null-length `Address` value.

This null-length `Address` value is identical to the one we used before
we adjusted `computeMinimumCoinForUTxO` to require a valid `Address`.

However, we were also able to adjust `performSelectionEmpty` so that it
no longer needs to validate minimum ada quantities of user-specified
outputs, and consequently we were able to reduce the dummy output's
`Coin` value to just `Coin 1`, which has the smallest space cost of
any non-zero `Coin` value.

This results in a further reduction in cost overestimation while
constructing change, which results in a lower cost when joining and
quitting stake pools.

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

@@ -1433,8 +1433,8 @@ spec = describe "SHELLEY_STAKE_POOLS" $ do
     costOfJoining :: Context -> Natural
     costOfJoining ctx =
         if _mainEra ctx >= ApiBabbage
-        then costOf (\coeff cst -> 487 * coeff + cst) ctx
-        else costOf (\coeff cst -> 483 * coeff + cst) ctx
+        then costOf (\coeff cst -> 454 * coeff + cst) ctx
+        else costOf (\coeff cst -> 450 * coeff + cst) ctx
 
     costOfQuitting :: Context -> Natural
     costOfQuitting ctx =