drm/amd/display: remove unused func declaration from resource headers

The function resource_validate_ctx_update_pointer_after_copy() is
declared in resource.h but never defined, therefore, remove its
declaration from headers.

Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Melissa Wen <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 		struct dc_state *context,
 		const struct resource_pool *pool);
 
-void resource_validate_ctx_update_pointer_after_copy(
-		const struct dc_state *src_ctx,
-		struct dc_state *dst_ctx);
-
 enum dc_status resource_map_clock_resources(
 		const struct dc *dc,
 		struct dc_state *context,