Find these lines in src/config/renewal.h and disable them by commenting them out.
Then recompile your server.
/// game renewal server mode
#define RENEWAL
/// renewal cast time
#define RENEWAL_CAST
/// renewal drop rate algorithms
#define RENEWAL_DROP
/// renewal exp rate algorithms
#define RENEWAL_EXP
/// renewal level modifier on damage
#define RENEWAL_LVDMG
/// renewal ASPD [malufett]
#define RENEWAL_ASPD