Changing SystemUiProxy to kotlin

> Simplifying some try-catch stamtements
> Removing unnecessary interface implementation
> Using kotlin native null check, which also prevents NullpointExeception
  when using calling methods from a non-main thread

Bug: 314010650
Flag: N/A
Test: Presubmit
Change-Id: I435ace5df8d7a19a8bba4099408f6cc7257d1f1f
2 files changed