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/FileSystem/Ext2FileSystem.cpp

@@ -59,9 +59,7 @@ Ext2FS::Ext2FS(OpenFileDescription& file_description)
 {
 }
 
-Ext2FS::~Ext2FS()
-{
-}
+Ext2FS::~Ext2FS() = default;
 
 ErrorOr<void> Ext2FS::flush_super_block()
 {