pip is not needed to run tests.

--- build-1.4.0/tox.ini.orig
+++ build-1.4.0/tox.ini
@@ -13,8 +13,6 @@
 [testenv]
 description =
     run test suite with {basepython}
-deps =
-    pip
 pass_env =
     LC_ALL
     PIP_*