Summary: On Android, the status bar color is not always black by default. The existing code causes the status bar to revert to black once the last `<StatusBar>` component is unmounted from the "stack". This diff reverts the bar background color to what it was before, instead of assuming black.
Reviewed By: yungsters
Differential Revision: D13368136
fbshipit-source-id: ef0154f776607b57bb9400b72d521f5f485b0075