Fix modelUnload deadlock

The concurrency policy for this module is that the lock should not be
held while calling stopRecognition and unloadModel into the HAL --
however, that was not being observed for unloadModel.

Update the framework state under the lock, and then drop it to call
unloadModel on the HAL interface. There are no post-conditions on the
STHAL call that the framework cares about, so this we don't need an
unloading state, and this is safe.

There could be an issue if we state protected the onModelUnloaded
callback, but the current implementation fails to do this regardless
(leaves it up to the callers), so it is not an issue.

Fixes: 374908863
Test: compiles
Flag: EXEMPT trivial bugfix
Change-Id: I625af495bb28baf6cdccd1916eda772889e71597