Remove mg_log_set_callback. Use MG_PUTCHAR macro instead

src/log.h

@@ -7,7 +7,6 @@ enum { MG_LL_NONE, MG_LL_ERROR, MG_LL_INFO, MG_LL_DEBUG, MG_LL_VERBOSE };
 void mg_log(const char *fmt, ...) PRINTF_LIKE(1, 2);
 bool mg_log_prefix(int ll, const char *file, int line, const char *fname);
 void mg_log_set(const char *spec);
-void mg_log_set_callback(void (*fn)(const void *, size_t, void *), void *param);
 void mg_hexdump(const void *buf, size_t len);
 
 #define MG_LOG(level, args)                                                \