clk: sunxi: Removed unused/incorrect sun6i-a31-apb2-clk driver

This driver does not match the hardware, which is actually compatible
to sun4i-a10-apb1-clk. Since we've switch to the correct one, drop
this driver.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>