oeqa/selftest/systemd_boot: Never use cleansstate in QA tests without special handling of SSTATE_DIR

Removing things straight from the live sstate directory is prone to issues
since other builds may be relying on the artefact presence.

Also, cleansstate is very slow on the huge sstate that the autobuilder has
on slow NFS drives. This may well be causing long buildtimes in oe-selftest
as the time taken to remove the artefact by be long.

(From meta-yocto rev: c4efa89f77e4d69826a9bbba47393ec737547469)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-yocto-bsp/lib/oeqa/selftest/cases/systemd_boot.py

@@ -44,7 +44,7 @@ class Systemdboot(OESelftestTestCase):
 
         # Ensure we're actually testing that this gets built and not that
         # it was around from an earlier build
-        bitbake('-c cleansstate systemd-boot')
+        bitbake('-c clean systemd-boot')
         runCmd('rm -f %s' % systemdbootfile)
 
         self._common_build()