[Misc] Also remove build fold in graphbolt and dgl_sparse in build_dgl.sh. (#6212)

Co-authored-by: Ubuntu <ubuntu@ip-172-31-28-63.ap-northeast-1.compute.internal>

script/build_dgl.sh

@@ -59,6 +59,8 @@ fi
 
 if [[ ${remove} == "YES" ]]; then
   rm -rf build
+  rm -rf graphbolt/build
+  rm -rf dgl_sparse/build
 fi
 
 if [[ -z ${build_type} ]]; then