adb_wait_for_device: Skip adb wait-for-device

This should still wait for the device to be attached and finished
booting, but will prevent no-output timeouts due to
`adb wait-for-device` never finishing.

The effect should be that, when an Android device is disconnected, the
"wait for device" step will run forever, or until the device
reconnects. This should prevent a disconnected device from spreading
purple all over the status page.

BUG=skia:

Review URL: https://codereview.chromium.org/1315753010

platform_tools/android/bin/adb_wait_for_device

@@ -9,8 +9,6 @@ source $SCRIPT_DIR/utils/setup_adb.sh
 set -e
 set -x
 
-$ADB $DEVICE_SERIAL wait-for-device
-
 while [ "$($ADB $DEVICE_SERIAL shell getprop sys.boot_completed | tr -d '\r')" != "1" ]; do
   sleep 5
 done