amdgpu/dc: drop display_pipe_clocks.c.

This code isn't used at all in the kernel tree, perhaps it can wait to
be imported when it is. It also does a lot of floating point calcs,
so probably good to drop it until it's needed and we can ensure
proper fpu accessors.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>