mantle/kola: remove sync workaround

The referenced issue in #1301
has long since been fixed.

mantle/kola/tests/upgrade/basic.go

@@ -178,12 +178,6 @@ func fcosUpgradeBasic(c cluster.TestCluster) {
  c.RunCmdSyncf(m, "ostree --repo=%s pull-local %s %s", ostreeRepo, tmprepo, ostreeref)
  }
 
- // XXX: This is to work around sysroot
- // remounting in libostree forcing a cache flush and blocking D-Bus.
- // Should drop this once we fix it more properly in {rpm-,}ostree.
- // https://github.com/coreos/coreos-assembler/issues/1301
- c.RunCmdSync(m, "time sudo sync")
-
  })
 
  c.Run("upgrade-from-previous", func(c cluster.TestCluster) {