Libraries: Use default constructors/destructors in LibGfx

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."

Userland/Libraries/LibGfx/FontDatabase.h

@@ -54,7 +54,7 @@ public:
 
 private:
     FontDatabase();
-    ~FontDatabase();
+    ~FontDatabase() = default;
 
     RefPtr<Typeface> get_or_create_typeface(const String& family, const String& variant);