Remove synchronized on method, loosen test

The synchronized on the method is a leftover. Loosening
the test still triggers the deadlock without the fix, it should
help on slow CI environments.

References #49

Author: acogoluegnes

src/main/java/com/rabbitmq/stream/impl/ConsumersCoordinator.java

@@ -720,7 +720,7 @@ void add(
       }
     }
 
-    synchronized void remove(SubscriptionTracker subscriptionTracker) {
+    void remove(SubscriptionTracker subscriptionTracker) {
       synchronized (this.owner) {
 
         // FIXME check manager is still open (not closed because of connection failure)

src/test/java/com/rabbitmq/stream/impl/ConsumersCoordinatorTest.java

@@ -1193,15 +1193,15 @@ void subscribeUnsubscribeInDifferentThreadsShouldNotDeadlock() throws Exception
       executorService.submit(
           () -> {
             int count = 0;
-            while (count++ < 100) {
+            while (count++ < 10) {
               subUnsub.run();
             }
             latch.countDown();
           });
       executorService.submit(
           () -> {
             int count = 0;
-            while (count++ < 100) {
+            while (count++ < 10) {
               subUnsub.run();
             }
             latch.countDown();