Well, the stubby looks like your AM/FM to me, and I'd just unscrew that if I were in your shoes if you don't want to listen to the radio. I'm guessing the base of it is a little wider because they put the Sat antenna in there. I wouldn't mess with that just because I don't think it will save much and could cause problems.
Car sat nav maps are usually stored on a DVD, hard drive, SD card, or other internal storage. I'm not aware of any that download the maps from an internet connection of some sort.
EDIT: I just realized you are probably asking if it receives the GPS signal there, and my guess would be yes, so that's another reason I wouldn't mess with it.
EDIT2: Looks like the GPS antenna is located on the drivers side dash.
That got me into trouble once because I had navigated to a hiking trail using my phone, which had internet access to download the route as I embarked, but had no internet when leaving the trailhead. I switched on my car sat nav which hadn't been updated in years, and it led me 50 miles ending on a cliff. Had to backtrack on fumes.
I came whipping around that corner at about 60 and this is where I stopped.
