Exporter.OpenTelemetryProtocol - GRPC - drop references to System.Net.Http.SocketsHttpHandler.Http2UnencryptedSupport

.NET Core 3.x is no longer supported

Author: Kielek

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/ExportClient/BaseOtlpGrpcExportClient.cs

@@ -20,8 +20,6 @@ protected BaseOtlpGrpcExportClient(OtlpExporterOptions options)
         Guard.ThrowIfNull(options);
         Guard.ThrowIfInvalidTimeout(options.TimeoutMilliseconds);
 
-        ExporterClientValidation.EnsureUnencryptedSupportIsEnabled(options);
-
         this.Endpoint = new UriBuilder(options.Endpoint).Uri;
         this.Headers = options.GetMetadataFromHeaders();
         this.TimeoutMilliseconds = options.TimeoutMilliseconds;