rm sone unused code

Device/Mask/DetectorMask.cpp

@@ -50,16 +50,6 @@ DetectorMask::DetectorMask(const DetectorMask& other)
 {
 }
 
-DetectorMask& DetectorMask::operator=(const DetectorMask& other)
-{
-    if (this != &other) {
-        m_stack = other.m_stack;
-        m_masked = other.m_masked;
-        m_number_of_masked_channels = other.m_number_of_masked_channels;
-    }
-    return *this;
-}
-
 void DetectorMask::addMask(const IShape2D& shape, bool mask_value)
 {
     m_stack.emplace_back(new MaskPattern(shape.clone(), mask_value));