Revert "Update notification expander background colors"

Revert submission 35133900-update-notif-expander-colors

Reason for revert: Droidmonitor initiated the revert due to http://b/442013003. Will verify through ABTD before submission.

Reverted changes: /q/submissionid:35133900-update-notif-expander-colors

Fix: 442013003

Change-Id: Iaa26958686c9232600a181339aaceb1e6e318585