Cleanup: Metal: Remove unused struct

This is no longer necessary since we do not use geometry shader
workarounds.

source/blender/gpu/metal/mtl_pso_descriptor_state.hh

@@ -76,47 +76,6 @@ struct MTLVertexBufferLayoutDescriptorPSO {
   }
 };
 
-/* SSBO attribute state caching. */
-struct MTLSSBOAttribute {
-
-  int mtl_attribute_index;
-  int vbo_id;
-  int attribute_offset;
-  int per_vertex_stride;
-  int attribute_format;
-  bool is_instance;
-
-  MTLSSBOAttribute() = default;
-  MTLSSBOAttribute(
-      int attribute_ind, int vertexbuffer_ind, int offset, int stride, int format, bool instanced)
-      : mtl_attribute_index(attribute_ind),
-        vbo_id(vertexbuffer_ind),
-        attribute_offset(offset),
-        per_vertex_stride(stride),
-        attribute_format(format),
-        is_instance(instanced)
-  {
-  }
-
-  bool operator==(const MTLSSBOAttribute &other) const
-  {
-    return (mtl_attribute_index == other.mtl_attribute_index && vbo_id == other.vbo_id &&
-            attribute_offset == other.attribute_offset &&
-            per_vertex_stride == other.per_vertex_stride &&
-            attribute_format == other.attribute_format && is_instance == other.is_instance);
-  }
-
-  void reset()
-  {
-    mtl_attribute_index = 0;
-    vbo_id = 0;
-    attribute_offset = 0;
-    per_vertex_stride = 0;
-    attribute_format = 0;
-    is_instance = false;
-  }
-};
-
 struct MTLVertexDescriptor {
 
   /* Core Vertex Attributes. */