Revert "Add VTS test for clearing buffer slots to Composer HIDL and AIDL"

This reverts commit ca3eef29.

NOTE: This is not a full revert, it leaves the production code in place and only reverts the VTS test changes.

Reason for revert: b/262370410

Test: atest VtsHalGraphicsComposerV2_1TargetTest on Oriole
Test: atest VtsHalGraphicsComposerV2_2TargetTest on Oriole
Test: atest VtsHalGraphicsComposerV2_3TargetTest on Oriole
Test: atest VtsHalGraphicsComposerV2_4TargetTest on Oriole
Bug: 262370410
Change-Id: Ie5ba7402cda2828ba33131d527ab0c3a66937648