Remove unused test code

test/test_api/import_tree_for_usages/__init__.py

@@ -1,4 +0,0 @@
-"""
-An import tree, for testing references.
-"""
-

test/test_api/import_tree_for_usages/a.py

@@ -1,4 +0,0 @@
-from . import b
-
-def foo():
-    b.bar()

test/test_api/import_tree_for_usages/b.py

@@ -1,2 +0,0 @@
-def bar():
-    pass