Remove the cfg argument from Step.Execute [#67]

This is the first step toward removing run.Config entirely. InitKube was
the only Step that even used cfg in its Execute function; the rest just
discarded it.

internal/run/uninstall_test.go

@@ -78,7 +78,7 @@ func (suite *UninstallTestSuite) TestPrepareAndExecute() {
 	expected := []string{"uninstall", "zayde_wølf_king"}
 	suite.Equal(expected, actual)
 
-	u.Execute(cfg)
+	u.Execute()
 }
 
 func (suite *UninstallTestSuite) TestPrepareDryRunFlag() {