Remove adding parent's presence for child FRUs

In the existing code, vpd-tool emplaces the parent FRU's presence for
child FRU whose "Present" property is not available on d-bus. This
gives a misleading information on presence state of non embedded FRU's,
which can either be present or absent on a machine.

Fix:
This commit modifies the vpd-tool code to print "Unknown" if the FRU's
Present property is not available on d-bus.

Test:
1. When Present property is not published on d-bus
vpd-tool -o -O /system/chassis/motherboard/powersupply0
[
    {
        "/system/chassis/motherboard/powersupply0": {
            "LocationCode": "U78DA.ND0.WZS0065-E0",
            "Present": "Unknown",
            "TYPE": "FRU",
            "type": "xyz.openbmc_project.Inventory.Item.PowerSupply"
        }
    }
]

2. When Present property is set to true on dbus
:~# vpd-tool -o -O /system/chassis/motherboard/powersupply0
[
    {
        "/system/chassis/motherboard/powersupply0": {
            "CC": "51DA",
            "DR": "IBM PS",
            "FN": "03FP221",
            "LocationCode": "U780C.ND0.RCH0014-E0",
            "PN": "03FP207",
            "Present": "true",
            "SN": "YL31KY12K0CX",
            "TYPE": "FRU",
            "type": "xyz.openbmc_project.Inventory.Item.PowerSupply"
        }
    }
]

3. When Present property is set to false on dbus
:~# vpd-tool -o -O /system/chassis/motherboard/powersupply0
[
    {
        "/system/chassis/motherboard/powersupply0": {
            "CC": "51DA",
            "DR": "IBM PS",
            "FN": "03FP221",
            "LocationCode": "U780C.ND0.RCH0014-E0",
            "PN": "03FP207",
            "Present": "false",
            "SN": "YL31KY12K0CX",
            "TYPE": "FRU",
            "type": "xyz.openbmc_project.Inventory.Item.PowerSupply"
        }
    }
]

Signed-off-by: Priyanga Ramasamy <priyanga24@in.ibm.com>
Change-Id: I4c8ce2141b9ae7c46f1421c59de5d627b8aad429
diff --git a/vpd_tool_impl.hpp b/vpd_tool_impl.hpp
index 669232a..16c3a34 100644
--- a/vpd_tool_impl.hpp
+++ b/vpd_tool_impl.hpp
@@ -132,11 +132,9 @@
     /**
      * @brief Get the json which has Present property value of the given fru.
      * @param[in] invPath - inventory path of the fru.
-     * @param[out] parentPresence - Update the parent fru's present property.
      * @return output json which has the Present property value.
      */
-    json getPresentPropJson(const std::string& invPath,
-                            std::string& parentPresence);
+    json getPresentPropJson(const std::string& invPath);
 
     /**
      * @brief Parse through the options to fix system VPD