v3d/compiler: remove return_channels from the shader key

This isn't used anywhere.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34742>

src/broadcom/compiler/v3d_compiler.h

@@ -413,7 +413,6 @@ struct v3d_key {
         } tex[V3D_MAX_TEXTURE_SAMPLERS];
         struct {
                 uint8_t return_size;
-                uint8_t return_channels;
         } sampler[V3D_MAX_TEXTURE_SAMPLERS];
 
         uint8_t num_tex_used;

src/broadcom/vulkan/v3dv_pipeline.c

@@ -980,9 +980,6 @@ pipeline_populate_v3d_key(struct v3d_key *key,
         sampler_idx++) {
       key->sampler[sampler_idx].return_size =
          sampler_map->return_size[sampler_idx];
-
-      key->sampler[sampler_idx].return_channels =
-         key->sampler[sampler_idx].return_size == 32 ? 4 : 2;
    }
 
    switch (p_stage->stage) {