init, Documentation: Remove ramdisk_blocksize mentions

init, Documentation: Remove ramdisk_blocksize mentions

The brd driver has never supported the ramdisk_blocksize kernel
parameter that was in the rd driver it replaced, so remove
mention of this parameter from comments and Documentation.

Commit 7b8ec5c4091b ("rewrite rd") replaced rd with brd, keeping
a brd_blocksize variable in struct brd_device but never using it.

Commit 153ca01bb7d8 ("brd: get rid of unused members from struct
brd_device") removed the unused variable.

Commit 7eefeabea2cd ("Documentation/blockdev/ramdisk.txt: updates")
removed mentions of ramdisk_blocksize from that file.

Signed-off-by: Robert Elliott <elliott@hpe.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>