Removes redundant code from JsonCamelCaseNamingPolicy.cs

Author: tcortega

src/libraries/System.Text.Json/Common/JsonCamelCaseNamingPolicy.cs

@@ -15,11 +15,7 @@ public override string ConvertName(string name)
 #if NETCOREAPP
             return string.Create(name.Length, name, (chars, name) =>
             {
-                name
-#if !NETCOREAPP
-                .AsSpan()
-#endif
-                .CopyTo(chars);
+                name.CopyTo(chars);
                 FixCasing(chars);
             });
 #else