Remove Boost conditional compilation.

Boost is currently at version 106200 in the depends subsystem
so it is safe to remove code the refers to earlier versions.

This closes #2445

src/wallet/walletdb.cpp

@@ -968,11 +968,7 @@ bool BackupWallet(const CWallet& wallet, const string& strDest)
                     pathDest /= wallet.strWalletFile;
 
                 try {
-#if BOOST_VERSION >= 104000
                     boost::filesystem::copy_file(pathSrc, pathDest, boost::filesystem::copy_option::overwrite_if_exists);
-#else
-                    boost::filesystem::copy_file(pathSrc, pathDest);
-#endif
                     LogPrintf("copied wallet.dat to %s\n", pathDest.string());
                     return true;
                 } catch (const boost::filesystem::filesystem_error& e) {