SpellCheckerSession: Fix brittle finalizer pattern.

Always call super.finalize, also make sure super-class finalizers
are called last (i.e in reverse order of construction). While we're
here, we can switch to dalvik.system.CloseGuard to warn if the object
hasn't been properly closed.

Test: make
Bug: 35609098
Change-Id: I4e00c3a2cec93d1dacff20546e481fe757279661