remoteproc/ste: remove abandoned include file

STE modem driver has been removed in 2016. This include has no
users since then.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Cc: Jean Delvare <jdelvare@suse.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Ohad Ben-Cohen <ohad@wizery.com>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Suman Anna <s-anna@ti.com>
Acked-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>