selftest: use INIT_MANAGER to enable systemd instead of custom settings

This is already done in most of selftest; these two were the last
holdouts I could fine.

Hopefully this improves sstate reuse as well.

(From OE-Core rev: 98f2feeea8f54f899e831a13191578b94cde7670)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/selftest/cases/imagefeatures.py

@@ -250,12 +250,7 @@ USERADD_GID_TABLES += "files/static-group"
 DISTRO_FEATURES:append = " pam opengl wayland"
 
 # Switch to systemd
-DISTRO_FEATURES:append = " systemd usrmerge"
-VIRTUAL-RUNTIME_init_manager = "systemd"
-VIRTUAL-RUNTIME_initscripts = ""
-VIRTUAL-RUNTIME_syslog = ""
-VIRTUAL-RUNTIME_login_manager = "shadow-base"
-DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit"
+INIT_MANAGER = "systemd"
 
 # Replace busybox
 PREFERRED_PROVIDER_virtual/base-utils = "packagegroup-core-base-utils"

meta/lib/oeqa/selftest/cases/runtime_test.py

@@ -310,10 +310,7 @@ class Postinst(OESelftestTestCase):
                 features += 'IMAGE_FEATURES += "package-management empty-root-password"\n'
                 features += 'PACKAGE_CLASSES = "%s"\n' % classes
                 if init_manager == "systemd":
-                    features += 'DISTRO_FEATURES:append = " systemd usrmerge"\n'
-                    features += 'VIRTUAL-RUNTIME_init_manager = "systemd"\n'
-                    features += 'DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit"\n'
-                    features += 'VIRTUAL-RUNTIME_initscripts = ""\n'
+                    features += 'INIT_MANAGER = "systemd"\n'
                 self.write_config(features)
 
                 bitbake('core-image-minimal')