readahead: when doing a system update drop readahead file

Makefile.am

@@ -2379,6 +2379,7 @@ rootlibexec_PROGRAMS += \
 	systemd-readahead-replay
 
 dist_systemunit_DATA += \
+	units/systemd-readahead-drop.service \
 	units/systemd-readahead-done.timer
 
 nodist_systemunit_DATA += \

units/systemd-readahead-collect.service.in

@@ -22,3 +22,4 @@ OOMScoreAdjust=1000
 
 [Install]
 WantedBy=default.target
+Also=systemd-readahead-drop.service

units/systemd-readahead-drop.service

@@ -0,0 +1,18 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Drop Read-Ahead Data
+ConditionPathExists=/.readahead
+
+[Service]
+Type=oneshot
+ExecStart=/bin/rm -f /.readahead
+
+[Install]
+WantedBy=system-update.target
+Also=systemd-readahead-collect.service