Revert "block: Make REQ_OP_ZONE_FINISH a write operation"

This reverts commit 4072d512 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: I2bded9babac775fa77757c45a368f8a93a96fe80
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>