Remove the virtual specifier for functions with the override specifier

`override` guarantees that the function is virtual (in addition
to that the function is overriding a virtual function from a base
class).

src/dbwrapper.cpp

@@ -19,7 +19,7 @@ class CBitcoinLevelDBLogger : public leveldb::Logger {
 public:
     // This code is adapted from posix_logger.h, which is why it is using vsprintf.
     // Please do not do this in normal code
-    virtual void Logv(const char * format, va_list ap) override {
+    void Logv(const char * format, va_list ap) override {
             if (!LogAcceptCategory(BCLog::LEVELDB)) {
                 return;
             }