Clean up code (1/2)

We clean up the unused darkModeSnapshotRestorer, because this is no
longer used in the section views on the main surface.
When moving the dark mode toggle from the section view to the color
settings screen, we missed to also remove the unused dark mode
restorer.
Make sure we use application context instead of Activity

Test: Build success
Fixes: 306018743
Flag: NONE
Change-Id: I2924737625ae17576fa2681268e331a19b9a228d