Minor refactoring in thresholds

No functional changes

Tested:
- All unit tests are passing

Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
Change-Id: I96360276cc7e7797a9e90a577804e94014e0bd91
diff --git a/src/numeric_threshold.cpp b/src/numeric_threshold.cpp
index 9bda509..24683a2 100644
--- a/src/numeric_threshold.cpp
+++ b/src/numeric_threshold.cpp
@@ -22,18 +22,18 @@
 
 void NumericThreshold::initialize()
 {
-    ThresholdOperations().initialize(this);
+    ThresholdOperations::initialize(this);
 }
 
 void NumericThreshold::updateSensors(Sensors newSensors)
 {
-    ThresholdOperations().updateSensors(this, std::move(newSensors));
+    ThresholdOperations::updateSensors(this, std::move(newSensors));
 }
 
 NumericThreshold::ThresholdDetail&
     NumericThreshold::getDetails(const interfaces::Sensor& sensor)
 {
-    return ThresholdOperations().getDetails(this, sensor);
+    return ThresholdOperations::getDetails(this, sensor);
 }
 
 std::shared_ptr<NumericThreshold::ThresholdDetail>