Fix: Address a few benign memory leaks

This patch is the result of static analysis identifying a number of
memory leaks. The leaks are all benign as they are a result of not
deallocating memory in the desctructor. The fix still has value as it
removes false positives in the static analysis.

src/sim/serialize.cc

@@ -613,6 +613,10 @@ Checkpoint::Checkpoint(const string &cpt_dir)
     }
 }
 
+Checkpoint::~Checkpoint()
+{
+    delete db;
+}
 
 bool
 Checkpoint::find(const string &section, const string &entry, string &value)

src/sim/serialize.hh

@@ -254,6 +254,7 @@ class Checkpoint
 
   public:
     Checkpoint(const std::string &cpt_dir);
+    ~Checkpoint();
 
     const std::string cptDir;