Nitrous: remove redundant system busy voting to cpupm driver

* we alreay vote system busy to notify cpupm driver in
nitrous_prepare_uart_tx_locked() function when BT UART TX and
nitrous_host_wake_isr() function when BT UART RX, no need to vote
system busy in nitrous_resume() function be called.

Bug: 187020537
Test: 1.run rock_bottom_p21.sh 2.Turn on the screen and stay at the
home screen

Change-Id: I6172bb7e15fc2768167fe628ca1e64dde99df070
Signed-off-by: jonerlin <jonerlin@google.com>