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/upgrade.go

@@ -45,7 +45,7 @@ func NewUpgrade(cfg env.Config) *Upgrade {
 }
 
 // Execute executes the `helm upgrade` command.
-func (u *Upgrade) Execute(_ Config) error {
+func (u *Upgrade) Execute() error {
 	return u.cmd.Run()
 }