load-fragment: Remove faulty assertion

Followup for 453cb5d01e

Fixes the following assertion:

"""
x86 130 ~/systemd ❯❯❯ meson compile -C build
ninja: Entering directory `/home/tfleig/systemd/build'
[2/5] Generating export-dbus-interfaces with a custom command
FAILED: interfaces
/home/tfleig/systemd/tools/dbus_exporter.py interfaces /home/tfleig/systemd/build/systemd /home/tfleig/systemd/build/systemd-homed /home/tfleig/systemd/build/systemd-hostnamed /home/tfleig/systemd/build/systemd-importd /home/tfleig/systemd/build/systemd-localed /home/tfleig/systemd/build/systemd-logind /home/tfleig/systemd/build/systemd-machined /home/tfleig/systemd/build/systemd-networkd /home/tfleig/systemd/build/systemd-oomd /home/tfleig/systemd/build/systemd-portabled /home/tfleig/systemd/build/systemd-resolved /home/tfleig/systemd/build/systemd-timedated
Assertion '__unique_prefix__expr_91' failed at src/core/load-fragment.c:3912, function config_parse_tasks_max(). Aborting.
Traceback (most recent call last):
  File "/home/tfleig/systemd/tools/dbus_exporter.py", line 45, in <module>
    main()
  File "/home/tfleig/systemd/tools/dbus_exporter.py", line 42, in main
    extract_interfaces_xml(args.output, exe)
  File "/home/tfleig/systemd/tools/dbus_exporter.py", line 9, in extract_interfaces_xml
    proc = run(
  File "/usr/lib64/python3.9/subprocess.py", line 528, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '[PosixPath('/home/tfleig/systemd/build/systemd'), '--bus-introspect', 'list']' died with <Signals.SIGABRT: 6>.
[4/5] Generating man/systemd.index.xml with a custom command
ninja: build stopped: subcommand failed.
"""

src/core/load-fragment.c

@@ -3909,7 +3909,7 @@ int config_parse_tasks_max(
                 void *userdata) {
 
         CGroupTasksMax *tasks_max = ASSERT_PTR(data);
-        const Unit *u = ASSERT_PTR(userdata);
+        const Unit *u = userdata;
         uint64_t v;
         int r;