ARM: SAMSUNG: remove keypad-core header in plat-samsung

Since keypad-core header is not used, this patch removes it.

Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>