drm/amd/display: Remove the repeated declaration

Function 'dc_power_down_on_boot' is declared twice, remove the
repeated declaration.

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dc.h

@@ -1069,8 +1069,6 @@ bool dc_resource_is_dsc_encoding_supported(const struct dc *dc);
  */
 bool dc_commit_state(struct dc *dc, struct dc_state *context);
 
-void dc_power_down_on_boot(struct dc *dc);
-
 struct dc_state *dc_create_state(struct dc *dc);
 struct dc_state *dc_copy_state(struct dc_state *src_ctx);
 void dc_retain_state(struct dc_state *context);