drm/amdgpu/gfx8: remove stale function declaration

This got leftover somehow when I cleaned this up.
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gfx_v8_0.h

@@ -26,6 +26,4 @@
 
 extern const struct amd_ip_funcs gfx_v8_0_ip_funcs;
 
-void gfx_v8_0_select_se_sh(struct amdgpu_device *adev, u32 se_num, u32 sh_num);
-
 #endif