Make LeaderScheduler::new_with_window_len private

It's useful for unit-testing, but generally isn't a variable
validators should be modifying. Blockstream and BlockstreamService
were the only ones using it. Switching them from a hard-coded 10
to the default didn't cause any test failures, so running with it.

src/blockstream.rs

@@ -181,7 +181,7 @@ mod test {
         genesis_block.slots_per_epoch = 2;
 
         let bank = Bank::new(&genesis_block);
-        let leader_scheduler = LeaderScheduler::new_with_window_len(10, &bank);
+        let leader_scheduler = LeaderScheduler::new_with_bank(&bank);
         let leader_scheduler = Arc::new(RwLock::new(leader_scheduler));
 
         // Set up blockstream

src/blockstream_service.rs

@@ -136,7 +136,7 @@ mod test {
         genesis_block.slots_per_epoch = 2;
 
         let bank = Bank::new(&genesis_block);
-        let leader_scheduler = LeaderScheduler::new_with_window_len(10, &bank);
+        let leader_scheduler = LeaderScheduler::new_with_bank(&bank);
         let leader_scheduler = Arc::new(RwLock::new(leader_scheduler));
 
         // Set up blockstream

src/leader_scheduler.rs

@@ -105,7 +105,9 @@ impl LeaderScheduler {
         }
     }
 
-    pub fn new_with_window_len(active_window_slot_len: u64, bank: &Bank) -> Self {
+    // Same as new_with_bank() but allows caller to override `active_window_slot_len`.
+    // Used by unit-tests.
+    fn new_with_window_len(active_window_slot_len: u64, bank: &Bank) -> Self {
         let config = LeaderSchedulerConfig::new(
             bank.ticks_per_slot(),
             bank.slots_per_epoch(),