Kernel: Use default constructors/destructors

https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#cother-other-default-operation-rules

"The compiler is more likely to get the default semantics right and
you cannot implement these functions better than the compiler."

Kernel/Devices/BlockDevice.cpp

@@ -24,9 +24,7 @@ void AsyncBlockDeviceRequest::start()
     m_block_device.start_request(*this);
 }
 
-BlockDevice::~BlockDevice()
-{
-}
+BlockDevice::~BlockDevice() = default;
 
 bool BlockDevice::read_block(u64 index, UserOrKernelBuffer& buffer)
 {