SurfaceControl: Allow calling destroy when mOwned is true

mOwned was just put in place to prevent the finalizer in SysUI
from destroying leashes, it was never meant to prevent explicit
calls to destroy. On another note we should probably remove destroy
or call it "release" but we can come back to that.

Change-Id: I72b0ab467105dc63094994de5482cec651fffaa3
Fixes: 113820778
Test: Builds