drm/radeon: remove unused declarations for radeon

radeon_combios_get_ext_tmds_info() has been removed since
commit fcec570b ("drm/radeon/kms: add support for
external tmds on legacy boards").

radeon_mst has been removed since
commit 01ad1d9c ("drm/radeon: Drop legacy MST support").

r600_hdmi_acr() has been removed since
commit 64424d6e ("radeon/audio: consolidate update_acr()
functions (v2)").

So remove the declarations for them from header file.
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220913024847.552254-4-cuigaosheng1@huawei.com

drivers/gpu/drm/radeon/radeon.h

@@ -116,7 +116,6 @@ extern int radeon_use_pflipirq;
 extern int radeon_bapm;
 extern int radeon_backlight;
 extern int radeon_auxch;
-extern int radeon_mst;
 extern int radeon_uvd;
 extern int radeon_vce;
 extern int radeon_si_support;
@@ -2950,8 +2949,6 @@ struct radeon_hdmi_acr {
 
 };
 
-extern struct radeon_hdmi_acr r600_hdmi_acr(uint32_t clock);
-
 extern u32 r6xx_remap_render_backend(struct radeon_device *rdev,
 				     u32 tiling_pipe_num,
 				     u32 max_rb_num,

drivers/gpu/drm/radeon/radeon_mode.h

@@ -874,7 +874,6 @@ extern struct radeon_encoder_tv_dac *
 radeon_atombios_get_tv_dac_info(struct radeon_encoder *encoder);
 extern struct radeon_encoder_lvds *
 radeon_combios_get_lvds_info(struct radeon_encoder *encoder);
-extern void radeon_combios_get_ext_tmds_info(struct radeon_encoder *encoder);
 extern struct radeon_encoder_tv_dac *
 radeon_combios_get_tv_dac_info(struct radeon_encoder *encoder);
 extern struct radeon_encoder_primary_dac *