nvmes.hpp: clean up unused member

clang-tidy issues the following warning:
```
../nvmes.hpp:63:23: warning: private field 'bus' is not used [-Wunused-private-field]
   63 |     sdbusplus::bus_t& bus;
```

Clean up the unused member.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ifba2ac63c2e8f93a89bf7d58024ff544defac3d0
diff --git a/nvmes.hpp b/nvmes.hpp
index 92dfc6f..eae8098 100644
--- a/nvmes.hpp
+++ b/nvmes.hpp
@@ -42,7 +42,7 @@
      * @param[in] objPath - The Dbus path of nvme
      */
     NvmeSSD(sdbusplus::bus_t& bus, const char* objPath) :
-        NvmeIfaces(bus, objPath), bus(bus)
+        NvmeIfaces(bus, objPath)
     {
         ValueIface::unit(Unit::DegreesC);
     }
@@ -58,9 +58,6 @@
     void setSensorMaxMin(int8_t maxValue, int8_t minValue);
     /** @brief Set Sensor Availability to D-bus */
     void setSensorAvailability(bool avail);
-
-  private:
-    sdbusplus::bus_t& bus;
 };
 } // namespace nvme
 } // namespace phosphor