ARM: dts: exynos: Remove exynos4415.dtsi

There are no boards in mainline using exynos4415.dtsi.  These DTSIs
were not tested for long.  I am also not aware of any popular out-of-tree
boards using this (except consumer devices released by Samsung but those
cannot use mainline).

Keeping Exynos4415 costs some useless effort so remove it.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>