Delete MemoryExtensions.AsBytes (dotnet/coreclr#17245)

Moved to MemoryMarshal

Signed-off-by: dotnet-bot-corefx-mirror <dotnet-bot@microsoft.com>

Author: jkotas

src/Common/src/CoreLib/System/MemoryExtensions.Fast.cs

@@ -356,52 +356,6 @@ public static bool StartsWith(this ReadOnlySpan<char> span, ReadOnlySpan<char> v
             }
         }
 
-        /// <summary>
-        /// Casts a Span of one primitive type <typeparamref name="T"/> to Span of bytes.
-        /// That type may not contain pointers or references. This is checked at runtime in order to preserve type safety.
-        /// </summary>
-        /// <param name="span">The source slice, of type <typeparamref name="T"/>.</param>
-        /// <exception cref="System.ArgumentException">
-        /// Thrown when <typeparamref name="T"/> contains pointers.
-        /// </exception>
-        /// <exception cref="System.OverflowException">
-        /// Thrown if the Length property of the new Span would exceed Int32.MaxValue.
-        /// </exception>
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static Span<byte> AsBytes<T>(this Span<T> span)
-            where T : struct
-        {
-            if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
-                ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(T));
-
-            return new Span<byte>(
-                ref Unsafe.As<T, byte>(ref MemoryMarshal.GetReference(span)),
-                checked(span.Length * Unsafe.SizeOf<T>()));
-        }
-
-        /// <summary>
-        /// Casts a ReadOnlySpan of one primitive type <typeparamref name="T"/> to ReadOnlySpan of bytes.
-        /// That type may not contain pointers or references. This is checked at runtime in order to preserve type safety.
-        /// </summary>
-        /// <param name="span">The source slice, of type <typeparamref name="T"/>.</param>
-        /// <exception cref="System.ArgumentException">
-        /// Thrown when <typeparamref name="T"/> contains pointers.
-        /// </exception>
-        /// <exception cref="System.OverflowException">
-        /// Thrown if the Length property of the new Span would exceed Int32.MaxValue.
-        /// </exception>
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static ReadOnlySpan<byte> AsBytes<T>(this ReadOnlySpan<T> span)
-            where T : struct
-        {
-            if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
-                ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(T));
-
-            return new ReadOnlySpan<byte>(
-                ref Unsafe.As<T, byte>(ref MemoryMarshal.GetReference(span)),
-                checked(span.Length * Unsafe.SizeOf<T>()));
-        }
-
         /// <summary>
         /// Creates a new span over the portion of the target array.
         /// </summary>