Disable enable_notifications_simulate_slow_measure flag for ExpandableNotificationRowTest

This test was failing when running it locally on a dev device, because
there was no value specified for this classic flag.

Test: atest ExpandableNotificationRowTest
Bug: 316157842
Flag: LEGACY com.android.systemui.flags.enable_notifications_simulate_slow_measure DISABLED
Change-Id: I178a6a4d7c74ba0e2eced6401bf6abb3a1c9357f