Fix update_prebuilts.py

Remove reference to args.stx left by If2d2369387e57c1e35d35b5982475d5970169980.

Test: ./update-prebuilts.py -p 6500461
Change-Id: Ifb37cc24fa0535c3918cc66ba4a1df39147063a8
Merged-In: I7c2e9b09ab0de36e352db16186288b0c4908f7b4
1 file changed