Input: remove no longer used power.c handler

Delete the never-compiled source file drivers/input/power.c, and
remove its entry from the corresponding Makefile, as there is no
Kconfig file that refers to the config option INPUT_POWER

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>