Revert "cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath."

This reverts commit 742300e3 which is
commit a738c93f

 upstream.

It is reported to cause problems in older kernels, so revert it for now
until we can figure it out...

Reported-by: Salvatore Bonaccorso <carnil@debian.org>
Link: https://lore.kernel.org/r/YG7r0UaivWZL762N@eldamar.lan
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Aurelien Aptel <aaptel@suse.com>
Cc: Steve French <stfrench@microsoft.com>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>