[ARM] sa1100: remove unused collie_pm.c

This file was never enabled in the mainline kernel, new ongoing work on
battery driver by Thomas Kunze makes it completely obsolete, so remove
it now.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Eric Miao <eric.miao@marvell.com>