BTA_SYS_EVT_DISABLED_EVT only ever comes in the HW_STOPPING state

it's only initated from bta_sys_hw_api_disable
bta_sys_hw_api_disable sets the state to HW_STOPPING

so remove this state and go there directly

Bug: 159815595
Tag: #refactor
Test: compile & verify basic functions working
Change-Id: I53c429bf05307a22256cd61885cfc5b263484128