ARM: plat-versatile: remove stale clock header

All the Versatile platforms (Integrator, Versatile, RealView
Versatile Express) have been migrated to use the drivers/clk
subsystem. Clean out this header that is not referenced
anywhere anymore.

Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>