pip is not needed to run tests.

--- hupper-1.12.1/tox.ini.orig
+++ hupper-1.12.1/tox.ini
@@ -6,9 +6,6 @@
 
 isolated_build = true
 
-requires =
-    pip >= 19
-
 [testenv]
 commands =
     py.test --cov --cov-report= {posargs:}