Remove ISample.Length

This has not been populated for a while and is not used osu! side.
Rather than having an incorrectly zero value, let's remove it for now.

Author: peppy

osu.Framework/Audio/Sample/ISample.cs

@@ -15,11 +15,6 @@ public interface ISample : IAdjustableAudioComponent
         /// </summary>
         string Name { get; }
 
-        /// <summary>
-        /// The length in milliseconds of this <see cref="ISample"/>.
-        /// </summary>
-        double Length { get; }
-
         /// <summary>
         /// The number of times this sample (as identified by name) can be played back concurrently.
         /// </summary>

osu.Framework/Audio/Sample/Sample.cs

@@ -19,7 +19,6 @@ protected Sample(string name)
             Name = name;
         }
 
-        public double Length { get; protected set; }
         public Bindable<int> PlaybackConcurrency { get; } = new Bindable<int>(DEFAULT_CONCURRENCY);
 
         internal Action<Sample> OnPlay;

osu.Framework/Graphics/Audio/DrawableSample.cs

@@ -51,8 +51,6 @@ public SampleChannel GetChannel()
 
         string ISample.Name => sample.Name;
 
-        public double Length => sample.Length;
-
         public Bindable<int> PlaybackConcurrency { get; } = new Bindable<int>(Sample.DEFAULT_CONCURRENCY);
 
         private IAudioMixer? mixer;