Fix duplicate symbols issues.

Index: src/c64dtv/c64dtviec.c
--- src/c64dtv/c64dtviec.c.orig
+++ src/c64dtv/c64dtviec.c
@@ -113,11 +113,3 @@ void plus4tcbm_update_pc(uint8_t byte, unsigned int dn
 {
 }
 
-void parallel_cable_drive_write(int port, uint8_t data, int handshake, unsigned int dnr)
-{
-}
-
-uint8_t parallel_cable_drive_read(int port, int handshake)
-{
-    return 0;
-}
