Revert "block: prepare I/O context code for BFQ-v5 for 3.0"

This reverts commit 4aa8b63a3d032d221b9d4dcfcd4f8695244498b7.

Conflicts:
	block/Kconfig.iosched

Change-Id: I549c3801af90771724699e17998055b7d42e4c68