Remove unnecessary local variant definitation.

'Vector<DisplayState> displays' has been not used in the approach of
SurfaceFlinger::initializeDisplays(), so just remove it.

Test: atest SurfaceFlinger_InitializeDisplaysTest

Change-Id: I6bb063ccef487ab23bc97e72e342353bdcaea748
Signed-off-by: jiayongqiang <jiayongqiang@xiaomi.com>