openjdk: 14.0.2 -> 15.0.1

* update two explicit references to jdk14 to just jdk, which no longer
  points at jdk8 after #89731.

* patch an explicit -XX:+UseConcMarkSweepGC to -XX:UseG1GC, as the
  former now throws an error (after having been deprecated since jdk 9)

pkgs/development/compilers/openjdk/darwin/default.nix

@@ -7,11 +7,11 @@ let
   };
 
   jdk = stdenv.mkDerivation rec {
-    name = "zulu14.28.21-ca-jdk14.0.1";
+    name = "zulu15.28.51-ca-jdk15.0.1";
 
     src = fetchurl {
       url = "https://cdn.azul.com/zulu/bin/${name}-macosx_x64.tar.gz";
-      sha256 = "1pc0y3fxhlf42a51qbdha1fabci61yzq70kk5c1rzk0ai78d92q8";
+      sha256 = "0h738pbnwcn7pjp0qyryzazqj5nw5sy2f8l0ycl39crm9ia6akvh";
       curlOpts = "-H Referer:https://www.azul.com/downloads/zulu/";
     };