Revert "MaybeNullWhen(false)"

This reverts commit 4813528.

src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs

@@ -54,7 +54,7 @@ public partial interface IConfigurationProvider
         Microsoft.Extensions.Primitives.IChangeToken GetReloadToken();
         void Load();
         void Set(string key, string? value);
-        bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value);
+        bool TryGet(string key, out string? value);
     }
     public partial interface IConfigurationRoot : Microsoft.Extensions.Configuration.IConfiguration
     {

src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs

@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.Extensions.Configuration
@@ -18,7 +17,7 @@ public interface IConfigurationProvider
         /// <param name="key">The key.</param>
         /// <param name="value">The value.</param>
         /// <returns><c>True</c> if a value for the specified key was found, otherwise <c>false</c>.</returns>
-        bool TryGet(string key, [MaybeNullWhen(false)] out string value);
+        bool TryGet(string key, out string? value);
 
         /// <summary>
         /// Sets a configuration value for the specified key.

src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs

@@ -68,7 +68,7 @@ public virtual void Load() { }
         protected void OnReload() { }
         public virtual void Set(string key, string? value) { }
         public override string ToString() { throw null; }
-        public virtual bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value) { throw null; }
+        public virtual bool TryGet(string key, out string? value) { throw null; }
     }
     public partial class ConfigurationReloadToken : Microsoft.Extensions.Primitives.IChangeToken
     {

src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using Microsoft.Extensions.Primitives;
 
@@ -36,7 +35,7 @@ protected ConfigurationProvider()
         /// <param name="key">The key to lookup.</param>
         /// <param name="value">The value found at key if one is found.</param>
         /// <returns>True if key has a value, false otherwise.</returns>
-        public virtual bool TryGet(string key, [MaybeNullWhen(false)] out string value)
+        public virtual bool TryGet(string key, out string? value)
             => Data.TryGetValue(key, out value);
 
         /// <summary>