Cleanup: Remove unused mesh dirty flags

These were only set in two places. One was related to "tessellated loop
normal", and the other derived corner normals. The values were never
checked though, after 59343ee162. The handling of dirty face
corner normals is clearly problematic, but in the future it should be
handled like the normal layers on the other domains instead.

Ref D14154, T95839

source/blender/blenkernel/intern/mesh.cc

@@ -1975,8 +1975,6 @@ void BKE_mesh_calc_normals_split_ex(Mesh *mesh, MLoopNorSpaceArray *r_lnors_spac
                               nullptr);
 
   BKE_mesh_assert_normals_dirty_or_calculated(mesh);
-
-  mesh->runtime.cd_dirty_loop &= ~CD_MASK_NORMAL;
 }
 
 void BKE_mesh_calc_normals_split(Mesh *mesh)

source/blender/makesdna/DNA_mesh_types.h

@@ -135,17 +135,6 @@ typedef struct Mesh_Runtime {
   float (*poly_normals)[3];
 
   void *_pad2;
-
-  /**
-   * Used to mark when derived data needs to be recalculated for a certain layer.
-   * Currently only normals.
-   */
-
-  int64_t cd_dirty_vert;
-  int64_t cd_dirty_edge;
-  int64_t cd_dirty_loop;
-  int64_t cd_dirty_poly;
-
 } Mesh_Runtime;
 
 typedef struct Mesh {

source/blender/modifiers/intern/MOD_uvproject.c

@@ -285,9 +285,6 @@ static Mesh *uvprojectModifier_do(UVProjectModifierData *umd,
 
   mesh->runtime.is_original = false;
 
-  /* Mark tessellated CD layers as dirty. */
-  mesh->runtime.cd_dirty_vert |= CD_MASK_TESSLOOPNORMAL;
-
   return mesh;
 }