[banden]

You are going to need to remount the partition as read/write, make the changes and then remount it as read again. Below should be the instructions for you to follow to remove those two objects you specified. This should be doable from a Terminal app on the device:

$ su
# mount -o remount,rw -t yaffs2 /dev/block/mtdblock4 /system
# rm system/app/Maps.apk
# rm data/app/com.google.android.maps.apk
# mount -o ro,remount -t yaffs2 /dev/block/mtdblock4 /system

NOTE: Be careful! You run the risk of damaging/bricking the phone whenever you go into Superuser permissions as you have full permission to modify every aspect of your operating system and the files contained in it. It's your own fault if you break something.