Apply suggestions from code review

Co-Authored-By: dkanada <dkanada@users.noreply.github.com>

Emby.Server.Implementations/Session/SessionManager.cs

@@ -102,17 +102,17 @@ namespace Emby.Server.Implementations.Session
         public event EventHandler<GenericEventArgs<AuthenticationResult>> AuthenticationSucceeded;
 
         /// <summary>
-        /// Occurs when [playback start].
+        /// Occurs when playback has started.
         /// </summary>
         public event EventHandler<PlaybackProgressEventArgs> PlaybackStart;
 
         /// <summary>
-        /// Occurs when [playback progress].
+        /// Occurs when playback has progressed.
         /// </summary>
         public event EventHandler<PlaybackProgressEventArgs> PlaybackProgress;
 
         /// <summary>
-        /// Occurs when [playback stopped].
+        /// Occurs when playback has stopped.
         /// </summary>
         public event EventHandler<PlaybackStopEventArgs> PlaybackStopped;