Remove getInternalDisplayToken usage from test app

SilkFX test app was using internal display token to set the hdr
listener. This isn't really needed since it was just logging data and
not actually testing anything.

The other usage was for display brightness, but calling
DM.setTemporaryBrightness will already handle it

Test: Builds
Bug: 242714168
Change-Id: I335ff21774b965d2f8bfdacacc5e10bd34e394f0