phosphor-state-manager: remove useless target symlink

We do not need to create symlinks to instantiate targets.  Remove
the one for `obmc-bmc-service-quiesce@.target`.

Tested:

```
root@witherspoon:/lib/systemd/system# systemctl start obmc-bmc-service-quiesce@0.target
root@witherspoon:~# obmcutil state
CurrentBMCState     : xyz.openbmc_project.State.BMC.BMCState.Quiesced
CurrentPowerState   : xyz.openbmc_project.State.Chassis.PowerState.Off
CurrentHostState    : xyz.openbmc_project.State.Host.HostState.Off
BootProgress        : xyz.openbmc_project.State.Boot.Progress.ProgressStages.Unspecified
OperatingSystemState: xyz.openbmc_project.State.OperatingSystem.Status.OSStatus.Inactive
```

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I73719f8cbce7ff3e01be868f471627c7acc2f6ca