systemd: 253.5 -> 253.6

Allows us to drop a patch

Also fixes systemd-repart being able to run in nix-build

pkgs/os-specific/linux/systemd/default.nix

@@ -145,7 +145,7 @@ assert withUkify -> withEfi;
 let
   wantCurl = withRemote || withImportd;
   wantGcrypt = withResolved || withImportd;
-  version = "253.5";
+  version = "253.6";
 
   # Bump this variable on every (major) version change. See below (in the meson options list) for why.
   # command:
@@ -162,7 +162,7 @@ stdenv.mkDerivation (finalAttrs: {
     owner = "systemd";
     repo = "systemd-stable";
     rev = "v${version}";
-    hash = "sha256-B3A9AvpfZ8SYsiZvHnWO4RHs1/6EdczWF2NmrSqxQ7c=";
+    hash = "sha256-LZs6QuBe23W643bTuz+MD2pzHiapsBJBHoFXi/QjzG4=";
   };
 
   # On major changes, or when otherwise required, you *must* reformat the patches,
@@ -190,13 +190,6 @@ stdenv.mkDerivation (finalAttrs: {
     ./0017-core-don-t-taint-on-unmerged-usr.patch
     ./0018-tpm2_context_init-fix-driver-name-checking.patch
     ./0019-bootctl-also-print-efi-files-not-owned-by-systemd-in.patch
-
-    # https://github.com/systemd/systemd/pull/28000
-    (fetchpatch {
-      name = "fix-service-exit";
-      url = "https://github.com/systemd/systemd/commit/5f7f82ba625ee48d662c1f0286f44b8b0918d05d.patch";
-      sha256 = "sha256-pFRXpZjeVl5ZG/mOjHEuMg9zXq4Orwvdp+/LYTbR09I=";
-    })
   ] ++ lib.optional stdenv.hostPlatform.isMusl (
     let
       oe-core = fetchzip {