Use a plain string for helm.Config.Command [#9]

I'm leaving the no-op test file in place because my next step is to add
new behavior that will require testing.

internal/helm/config_test.go

@@ -12,17 +12,3 @@ type ConfigTestSuite struct {
 func TestConfigTestSuite(t *testing.T) {
 	suite.Run(t, new(ConfigTestSuite))
 }
-
-func (suite *ConfigTestSuite) TestHelmCommandDecodeSuccess() {
-	cmd := helmCommand("")
-	err := cmd.Decode("upgrade")
-	suite.Require().Nil(err)
-
-	suite.EqualValues(cmd, "upgrade")
-}
-
-func (suite *ConfigTestSuite) TestHelmCommandDecodeFailure() {
-	cmd := helmCommand("")
-	err := cmd.Decode("execute order 66")
-	suite.EqualError(err, "unknown command 'execute order 66'. If specified, command must be upgrade, delete, lint, or help")
-}