LU-17848 osd: purge key_rec() from dt API

LU-17848 osd: purge key_rec() from dt API

This is a pointless function pointer field that has
spawned a number of pointless function implementations.
Even the documentation has no idea why this exists.

Remove everything to do with key_rec().

Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I7f84853a3fa285bf2ac53661b30384d099be1b91
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55099
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>