LU-14031 ptlrpc: remove unused code at pinger

LU-14031 ptlrpc: remove unused code at pinger

The timeout_list was previously used for grant shrinking,
but right now is dead code.

HPE-bug-id: LUS-8520
Fixes: fc915a43786e ("LU-8708 osc: depart grant shrinking from pinger")
Signed-off-by: Alexander Boyko <alexander.boyko@hpe.com>
Change-Id: Ia7a77b4ac19da768ebe1b0879d7123941f4490b5
Reviewed-on: https://review.whamcloud.com/40243
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Aurelien Degremont <degremoa@amazon.com>
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>