remove the parameter usb_trans_info from the functions that dissect the
standard descriptors

usb_trans_info is a part of usb_conv_info, there's no need to have it as
a separate parameter

Change-Id: I3608c10543b896ca04c6062de23297d852dae31a
Reviewed-on: https://code.wireshark.org/review/3731
Reviewed-by: Martin Kaiser <wireshark@kaiser.cx>
Tested-by: Martin Kaiser <wireshark@kaiser.cx>