Do not declare USB support in the Emulator

Some Framework code assumes USB, but the Emulator does not
support USB connections. To work around this, the Emulator
includes a trivial UsbManager and indicates
'android.hardware.usb.accessory' support.

This situation is inconsistent and causes problems, including
CTS and CTS-Verifier failures.

This change removes the indication of
'android.hardware.usb.accessory' and corrects a Framework
NPE if USB support is queried relative to a null device.

BUG: 28088069
     b.android.com/234319

Change-Id: I9d35b6bb7788db08f8121755300384db9eb8baf9
(cherry picked from commit 0f7ca97a57200eb1e2f3fb0081722f5775a6a14b)