Remove unnecessary null checks in some places

Related to https://github.com/jellyfin/jellyfin/issues/2149

Jellyfin.Api/Helpers/MediaInfoHelper.cs

@@ -554,7 +554,7 @@ namespace Jellyfin.Api.Helpers
         private long? GetMaxBitrate(long? clientMaxBitrate, User user, string ipAddress)
         {
             var maxBitrate = clientMaxBitrate;
-            var remoteClientMaxBitrate = user?.RemoteClientBitrateLimit ?? 0;
+            var remoteClientMaxBitrate = user.RemoteClientBitrateLimit ?? 0;
 
             if (remoteClientMaxBitrate <= 0)
             {

Jellyfin.Api/Helpers/TranscodingJobHelper.cs

@@ -740,10 +740,7 @@ namespace Jellyfin.Api.Helpers
         /// <param name="state">The state.</param>
         private void OnFfMpegProcessExited(Process process, TranscodingJobDto job, StreamState state)
         {
-            if (job != null)
-            {
-                job.HasExited = true;
-            }
+            job.HasExited = true;
 
             _logger.LogDebug("Disposing stream resources");
             state.Dispose();

Jellyfin.Server.Implementations/Users/UserManager.cs

@@ -799,7 +799,7 @@ namespace Jellyfin.Server.Implementations.Users
 
         private IList<IPasswordResetProvider> GetPasswordResetProviders(User user)
         {
-            var passwordResetProviderId = user?.PasswordResetProviderId;
+            var passwordResetProviderId = user.PasswordResetProviderId;
             var providers = _passwordResetProviders.Where(i => i.IsEnabled).ToArray();
 
             if (!string.IsNullOrEmpty(passwordResetProviderId))