Revert "block: add a new set_read_only method"

This reverts commit 2a0f8202 which is
commit e00adcad 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: I20342421827a743bfb159577aa151698b101d17d
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>