fix: Keep backward-compatibility broken after introduction of values file template (#257)

Fixes #249

tmpl/context.go

@@ -1,15 +1,5 @@
 package tmpl
 
-import "io/ioutil"
-
-var DefaultContext *Context
-
-func init() {
-	DefaultContext = &Context{
-		readFile: ioutil.ReadFile,
-	}
-}
-
 type Context struct {
 	readFile func(string) ([]byte, error)
 }