tree: use the basename for the entry removal

When we want to remove the file, use the basename as the name of the
entry to remove, instead of the full one, which includes the directories
we've inserted into the stack.

src/tree.c

@@ -1230,7 +1230,7 @@ int git_tree_create_updated(git_oid *out, git_repository *repo, git_tree *baseli
 				break;
 			}
 			case GIT_TREE_UPDATE_REMOVE:
-				error = git_treebuilder_remove(git_array_last(stack)->bld, update->path);
+				error = git_treebuilder_remove(git_array_last(stack)->bld, git_path_basename(update->path));
 				break;
 			default:
 				giterr_set(GITERR_TREE, "unkown action for update");