Update systemd-oomd defaults to friendlier values

- Remove swap policy. Default amount of swap (8GB?) is a lot lower than
  what we use internally with the swap policy. Which frequently leads to
  GNOME getting killed
  (e.g. https://bugzilla.redhat.com/show_bug.cgi?id=1941170, and other
  BZs not linked here). Internally we use 0.5x-1x size of physical memory
  for swap via swapfiles (this will be documented in systemd upstream).
  In simple cases of using more memory than is available (but without
  memory pressure), the Kernel OOM killer can handle killing the
  offending process.

- Expand the memory pressure policy to system.slice, user-.slice, and
  all user owned slices. Support for ManagedOOM*= on user services was
  added in https://github.com/systemd/systemd/pull/20690 which allows
  us to be more fine grained on the pressure monitoring at the user
  level. In addition to the system.slice and user-.slice PSI monitoring
  this should result in a better systemd-oomd experience for desktop
  systems.

10-oomd-per-slice-defaults.conf

@@ -1,3 +1,3 @@
-[Service]
+[Slice]
 ManagedOOMMemoryPressure=kill
 ManagedOOMMemoryPressureLimit=50%

10-oomd-root-slice-defaults.conf

@@ -1,2 +0,0 @@
-[Slice]
-ManagedOOMSwap=kill

systemd.spec

@@ -70,8 +70,7 @@ Source12:       systemd-user
 Source13:       libsystemd-shared.abignore
 
 Source14:       10-oomd-defaults.conf
-Source15:       10-oomd-root-slice-defaults.conf
-Source16:       10-oomd-user-service-defaults.conf
+Source15:       10-oomd-per-slice-defaults.conf
 
 Source21:       macros.sysusers
 Source22:       sysusers.attr
@@ -664,8 +663,9 @@ install -D -t %{buildroot}/usr/lib/systemd/ %{SOURCE3}
 
 # systemd-oomd default configuration
 install -Dm0644 -t %{buildroot}%{_prefix}/lib/systemd/oomd.conf.d/ %{SOURCE14}
-install -Dm0644 -t %{buildroot}%{system_unit_dir}/-.slice.d/ %{SOURCE15}
-install -Dm0644 -t %{buildroot}%{system_unit_dir}/user@.service.d/ %{SOURCE16}
+install -Dm0644 -t %{buildroot}%{system_unit_dir}/user-.slice.d/ %{SOURCE15}
+install -Dm0644 -t %{buildroot}%{system_unit_dir}/system.slice.d/ %{SOURCE15}
+install -Dm0644 -t %{buildroot}%{user_unit_dir}/slice.d/ %{SOURCE15}
 
 sed -i 's|#!/usr/bin/env python3|#!%{__python3}|' %{buildroot}/usr/lib/systemd/tests/run-unit-tests.py