Remove APTCA due to verification failures and deprecation of usage

Rx.NET/Source/src/AssemblyInfo.cs

@@ -7,5 +7,4 @@ using System.Security;
 
 [assembly: ComVisible(false)]
 [assembly: CLSCompliant(true)]
-[assembly: AllowPartiallyTrustedCallers]
-[assembly: NeutralResourcesLanguage("en-US")]
+[assembly: NeutralResourcesLanguage("en-US")]

Rx.NET/Source/src/Microsoft.Reactive.Testing/Properties/AssemblyInfo.cs

@@ -5,4 +5,3 @@ using System.Runtime.InteropServices;
 
 [assembly: ComVisible(false)]
 [assembly: CLSCompliant(true)]
-//[assembly: AllowPartiallyTrustedCallers]

Rx.NET/Source/tests/Tests.System.Reactive.ApiApprovals/Api/ApiApprovalTests.Aliases.approved.txt

@@ -2,7 +2,6 @@
 [assembly: System.Resources.NeutralResourcesLanguageAttribute("en-US")]
 [assembly: System.Runtime.InteropServices.ComVisibleAttribute(false)]
 [assembly: System.Runtime.Versioning.TargetFrameworkAttribute(".NETFramework,Version=v4.6", FrameworkDisplayName=".NET Framework 4.6")]
-[assembly: System.Security.AllowPartiallyTrustedCallersAttribute()]
 namespace System.Reactive.Linq
 {
     [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverageAttribute()]

Rx.NET/Source/tests/Tests.System.Reactive.ApiApprovals/Api/ApiApprovalTests.Core.approved.txt

@@ -4,7 +4,6 @@
 [assembly: System.Runtime.CompilerServices.InternalsVisibleToAttribute(@"Tests.System.Reactive.Uwp.DeviceRunner, PublicKey=00240000048000009400000006020000002400005253413100040000010001008f5cff058631087031f8350f30a36fa078027e5df2316b564352dc9eb7af7ce856016d3c5e9d058036fe73bb5c83987bd3fc0793fbe25d633cc4f37c2bd5f1d717cd2a81661bec08f0971dc6078e17bde372b89005e7738a0ebd501b896ca3e8315270ff64df7809dd912c372df61785a5085b3553b7872e39b1b1cc0ff5a6bc")]
 [assembly: System.Runtime.InteropServices.ComVisibleAttribute(false)]
 [assembly: System.Runtime.Versioning.TargetFrameworkAttribute(".NETFramework,Version=v4.6", FrameworkDisplayName=".NET Framework 4.6")]
-[assembly: System.Security.AllowPartiallyTrustedCallersAttribute()]
 namespace System
 {
     public class static ObservableExtensions