Remove invocation to 'cros_image_to_taget.py', which was deprecated on Feb 4.

Nightly failed because image_chromeos.py used
'cros_image_to_target.py' (this part still needs to examination ) to
image the machines.

Change-Id: I918e4a99a301ab6cc120fccd0b01c454597b8336
Reviewed-on: https://chrome-internal-review.googlesource.com/210135
Reviewed-by: Caroline Tice <cmtice@google.com>
Commit-Queue: Han Shen <shenhan@google.com>
Tested-by: Han Shen <shenhan@google.com>
1 file changed