LU-8837 ptlrpc: mark some functions as static

LU-8837 ptlrpc: mark some functions as static

The functions
 ptlrpc_start_threads,
 ptlrpc_start_thread,
 ptlrpc_stop_all_threads
 ptlrpc_nrs_policy_register
and
 ptlrpc_nrs_policy_register

are only used in the same file that defines them, so mark them as
'static' and remove the declarations from include files.

 ptlrpc_nrs_policy_unregister

is never used at all, so remove it completely.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Id7862b9da3c58ab980c0fcd4d07c1f119fbf7581
Reviewed-on: https://review.whamcloud.com/41947
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Aurelien Degremont <degremoa@amazon.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>