Allow UsbDeviceManager to start adbd again.

There's some weird state where if persist.sys.usb.config=none,adb, then
adbd won't get started. Give back adbd start permissions to
UsbDeviceManager to see if that fixes the issue.

Bug: 150130503

Test: adb shell su 0 setprop persist.sys.usb.config none,adb; adb reboot
adb should be online after.

Change-Id: I36c6ef4b20d58570a2d51ed70088ae5c54d6687d
Exempt-From-Owner-Approval: Fix adbd offline failure