Revert "Enable dark theme by defaut"

Revert submission 11049460-p20_dark_theme_by_default

Reason for revert: For P20 default dark mode will adopt the solution in b/154171431#comment19. System keep default light, let SUW to change the dark mode.
Reverted Changes:
I38c78a4ee:Enable dark theme by defaut
Ia3b0b43b5:Enable dark theme by defaut

Bug: 154171431
Change-Id: I04cc71a166093136ed2df5b16ad5e2a3a66af9fd
1 file changed