adb: don't reset usb when connecting it.

Calling libusb_reset_device() resets the usb connection with device
on linux platform. It can interfere with other usb interfaces and only
works on linux.
Removing it only affects when adb server is killed while doing IO with
device, which will be solved in later patches.

Bug: http://b/32952319
Test: none
Change-Id: I19522435eadd938ff95d49cbae3bcaa5c8f6d184