Remove C# code specific to .NET 3.5
The codebase has changed a lot since it was last able to compile
with .NET 3.5, so we don't need this vestigial code.
diff --git a/csharp/src/Google.Protobuf/Collections/MapField.cs b/csharp/src/Google.Protobuf/Collections/MapField.cs
index e5217f4..0f02d59 100644
--- a/csharp/src/Google.Protobuf/Collections/MapField.cs
+++ b/csharp/src/Google.Protobuf/Collections/MapField.cs
@@ -68,10 +68,7 @@
/// in future versions.
/// </para>
/// </remarks>
- public sealed class MapField<TKey, TValue> : IDeepCloneable<MapField<TKey, TValue>>, IDictionary<TKey, TValue>, IEquatable<MapField<TKey, TValue>>, IDictionary
-#if !NET35
- , IReadOnlyDictionary<TKey, TValue>
-#endif
+ public sealed class MapField<TKey, TValue> : IDeepCloneable<MapField<TKey, TValue>>, IDictionary<TKey, TValue>, IEquatable<MapField<TKey, TValue>>, IDictionary, IReadOnlyDictionary<TKey, TValue>
{
private static readonly EqualityComparer<TValue> ValueEqualityComparer = ProtobufEqualityComparers.GetEqualityComparer<TValue>();
private static readonly EqualityComparer<TKey> KeyEqualityComparer = ProtobufEqualityComparers.GetEqualityComparer<TKey>();
@@ -600,11 +597,8 @@
#endregion
#region IReadOnlyDictionary explicit interface implementation
-#if !NET35
IEnumerable<TKey> IReadOnlyDictionary<TKey, TValue>.Keys => Keys;
-
IEnumerable<TValue> IReadOnlyDictionary<TKey, TValue>.Values => Values;
-#endif
#endregion
private class DictionaryEnumerator : IDictionaryEnumerator
