mkosi: Drop orphan_file workaround

mkosi now handles this workaround itself internally.

mkosi.conf.d/10-centos/mkosi.conf.d/10-orphan-file.conf

@@ -1,13 +0,0 @@
-# SPDX-License-Identifier: LGPL-2.1-or-later
-
-[Match]
-ToolsTreeDistribution=|!centos
-ToolsTreeRelease=|!9
-
-[Build]
-# The kernel versions in CentOS Stream 9 doesn't support orphan_file, but later versions of
-# mkfs.ext4 enabled it by default, so we disable it explicitly. Except that older versions
-# of mkfs.ext4 don't know about "orphan_file" so we skip it on some tools tree variants where
-# we know "orphan_file" is not supported.
-Environment=
-        SYSTEMD_REPART_MKFS_OPTIONS_EXT4="-O ^orphan_file"