Most list "thingies" (sorry about the use of technical terms) have a "+" and "-" buttons at the bottom of the list. They usually allow you to add and delete/subtract items in the list.
Or you might try selecting a device you don't want/need and pressing the delete key.
I looked at Network Diagnostics.app [/System/Library/CoreServices/Network Diagnostics.app](which is what you get when you use the "Advanced" button in Networks Pref Panel) but that's not any help.
Normally, one would simply tell the iPad/iPhone/etc. to "forget" any particular Network. Obviously, that will be difficult if you no longer have the iDevice/computer... so...
I think your best bet is to do some kind of 'total memory purge' on the D-link. Strange as it seems, it must have memorized all the devices you ever connected with it. It's hard to believe its in any RAM but I suppose it could actually have an EPROM. More likely, it has a plist file that has continued to be copied with every OS update you've made. If that's where these items are stored, you should be able to see a plist file labeled something like: com.dlink... or com.D-link. You might need to also look in the /Library/Preferences directory.
Once found, just turn off the network (the D-link, anyway), move the plist file to the Desktop, and then trun the network devices (Cable Modem, D-link, extender) back on. Hopefully, that will force the D-link to recreate the plist file with fewer/no networked devices.
If all the above fails, take another cold shower and take your wife to lunch/dinner.