Minor fixes to the Fit Mesh tutorial (#1423)

Summary:
- Fix the numbers in the headers. Currently, there are no header number 2, the tutorial jump from 1 to 3.
- Clean some unnecessary code.

Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/1423

Reviewed By: shapovalov

Differential Revision: D42478609

Pulled By: bottler

fbshipit-source-id: c49fc10b7d38c3573c92fea737101e6c06bbea38

docs/tutorials/deform_source_mesh_to_target_mesh.ipynb

@@ -192,7 +192,7 @@
    "outputs": [],
    "source": [
     "# Load the dolphin mesh.\n",
-    "trg_obj = os.path.join('dolphin.obj')"
+    "trg_obj = 'dolphin.obj'"
    ]
   },
   {
@@ -247,7 +247,7 @@
     "id": "dYWDl4VGWHRK"
    },
    "source": [
-    "###  Visualize the source and target meshes"
+    "## 2. Visualize the source and target meshes"
    ]
   },
   {
@@ -485,7 +485,7 @@
     "final_verts = final_verts * scale + center\n",
     "\n",
     "# Store the predicted mesh using save_obj\n",
-    "final_obj = os.path.join('./', 'final_model.obj')\n",
+    "final_obj = 'final_model.obj'\n",
     "save_obj(final_obj, final_verts, final_faces)"
    ]
   },