control: Removed unused variables

Fix clang-tidy errors like:
```
../control/json/event.hpp:153:23: error: private field '_bus' is not used [-Werror,-Wunused-private-field]
```

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Ie57fbf73b16ce00b3eb67a0a0746f263ad333267
diff --git a/control/json/event.cpp b/control/json/event.cpp
index e4c9f8e..e129e1c 100644
--- a/control/json/event.cpp
+++ b/control/json/event.cpp
@@ -38,8 +38,7 @@
 
 Event::Event(const json& jsonObj, Manager* mgr,
              std::map<configKey, std::unique_ptr<Zone>>& zones) :
-    ConfigBase(jsonObj), _bus(util::SDBusPlus::getBus()), _manager(mgr),
-    _zones(zones)
+    ConfigBase(jsonObj), _manager(mgr), _zones(zones)
 {
     // Event groups are optional
     if (jsonObj.contains("groups"))