Remove CookieAuthenticationOptions.CookieSameSite which was never shipped as an RTM api

Author: Nate McMaster

src/Microsoft.AspNetCore.Authentication.Cookies/CookieAuthenticationOptions.cs

@@ -176,19 +176,6 @@ public CookieBuilder Cookie
         [Obsolete("This property is obsolete and will be removed in a future version. The recommended alternative is " + nameof(Cookie) + "." + nameof(CookieBuilder.Path) + ".")]
         public string CookiePath { get => Cookie.Path; set => Cookie.Path = value; }
 
-        /// <summary>
-        /// <para>
-        /// This property is obsolete and will be removed in a future version. The recommended alternative is <seealso cref="CookieBuilder.SameSite"/> on <see cref="Cookie"/>.
-        /// </para>
-        /// <para>
-        /// Determines if the browser should allow the cookie to be attached to same-site or cross-site requests. The
-        /// default is Lax, which means the cookie is only allowed to be attached to cross-site requests using safe
-        /// HTTP methods and same-site requests.
-        /// </para>
-        /// </summary>
-        [Obsolete("This property is obsolete and will be removed in a future version. The recommended alternative is " + nameof(Cookie) + "." + nameof(CookieBuilder.SameSite) + ".")]
-        public SameSiteMode CookieSameSite { get => Cookie.SameSite; set => Cookie.SameSite = value; }
-
         /// <summary>
         /// <para>
         /// This property is obsolete and will be removed in a future version. The recommended alternative is <seealso cref="CookieBuilder.HttpOnly"/> on <see cref="Cookie"/>.