Revert "bcache: Add a sample of userspace prefetch client"

euleros/rtos inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4LOJ6


CVE: NA

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This patch set introduce many conflicts while backporting mainline
bcache patches, revert it temporarily.

This reverts commit 87f258f0.

Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>