Fix Native tests for input are broken in postsubmit

For releaseChannel, if clear the token first then unregisterChannel.
It may access the null pointer while looking for the corresponding
window and input channel.

This would change test case to simply clear the channel and token.
So updateInfo would get a null token for testing if setInputWindow fine.

Bug: 117116942
Test: atest inputflinger_tests
Change-Id: I11853720795554e1d83dafb9f3df948b5ee7e90e