remove trans_info parameter from dissect_usb_unknown_descriptor()
remove now unused trans_info variable in mausb

Change-Id: I99df8a1ed039134c9448546d0f1a738f203f9610
Reviewed-on: https://code.wireshark.org/review/3785
Reviewed-by: Martin Kaiser <wireshark@kaiser.cx>
Tested-by: Martin Kaiser <wireshark@kaiser.cx>