Revert "block: Make REQ_OP_ZONE_FINISH a write operation"

This reverts commit 05ea5b2f which is
commit 3f66ccba upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Icd0549fe30f0038d9df41a959a40e67897ff4a82
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>