Additional simplifications: Remove NETCF, fix NET60 typo, consolidate NETCOREAPP2_1 pattern

Co-authored-by: adamhathcock <527620+adamhathcock@users.noreply.github.com>

src/SharpCompress/Compressors/Deflate/ZlibConstants.cs

@@ -108,13 +108,9 @@ internal static class ZlibConstants
     public const int Z_BUF_ERROR = -5;
 
     /// <summary>
-    /// The size of the working buffer used in the ZlibCodec class. Defaults to 8192 bytes.
+    /// The size of the working buffer used in the ZlibCodec class. Defaults to 16384 bytes.
     /// </summary>
-#if NETCF
-    public const int WorkingBufferSizeDefault = 8192;
-#else
     public const int WorkingBufferSizeDefault = 16384;
-#endif
 
     /// <summary>
     /// The minimum size of the working buffer used in the ZlibCodec class.  Currently it is 128 bytes.

src/SharpCompress/Compressors/Rar/MultiVolumeReadOnlyStream.cs

@@ -185,7 +185,7 @@ internal sealed class MultiVolumeReadOnlyStream : Stream, IStreamStack
         return totalRead;
     }
 
-#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+#if !LEGACY_DOTNET
     public override async System.Threading.Tasks.ValueTask<int> ReadAsync(
         Memory<byte> buffer,
         System.Threading.CancellationToken cancellationToken = default

src/SharpCompress/Compressors/Rar/RarBLAKE2spStream.cs

@@ -385,7 +385,7 @@ internal class RarBLAKE2spStream : RarStream, IStreamStack
         return result;
     }
 
-#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+#if !LEGACY_DOTNET
     public override async System.Threading.Tasks.ValueTask<int> ReadAsync(
         Memory<byte> buffer,
         System.Threading.CancellationToken cancellationToken = default

src/SharpCompress/Compressors/Rar/RarCrcStream.cs

@@ -129,7 +129,7 @@ internal class RarCrcStream : RarStream, IStreamStack
         return result;
     }
 
-#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+#if !LEGACY_DOTNET
     public override async System.Threading.Tasks.ValueTask<int> ReadAsync(
         Memory<byte> buffer,
         System.Threading.CancellationToken cancellationToken = default

src/SharpCompress/Compressors/Rar/RarStream.cs

@@ -189,7 +189,7 @@ internal class RarStream : Stream, IStreamStack
         return outTotal;
     }
 
-#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+#if !LEGACY_DOTNET
     public override async System.Threading.Tasks.ValueTask<int> ReadAsync(
         Memory<byte> buffer,
         System.Threading.CancellationToken cancellationToken = default

src/SharpCompress/Utility.cs

@@ -189,7 +189,7 @@ internal static class Utility
             }
         }
 
-#if NET60_OR_GREATER
+#if NET6_0_OR_GREATER
         public bool ReadFully(byte[] buffer)
         {
             try