Remove DEBUG from two exception messages

Author: lukebakken

projects/RabbitMQ.Client/client/impl/MainSession.cs

@@ -106,7 +106,7 @@ public void SetSessionClosing(bool closeIsServerInitiated)
             }
             else
             {
-                throw new InvalidOperationException("[DEBUG] couldn't enter semaphore");
+                throw new InvalidOperationException("couldn't enter semaphore");
             }
         }
 
@@ -129,7 +129,7 @@ public async Task SetSessionClosingAsync(bool closeIsServerInitiated)
             }
             else
             {
-                throw new InvalidOperationException("[DEBUG] couldn't async enter semaphore");
+                throw new InvalidOperationException("couldn't async enter semaphore");
             }
         }