composer: 2.4: vts: do not try to delay a config change outside a group

When switching to a new config, we can set the desiredTimeNanos to
be in the future only for configs within the same config groups.

Bug: 190250110
Test: atest VtsHalGraphicsComposerV2_4TargetTest
Change-Id: I5e292b656eccf6e90c06e08c6eb202d689b6f026