Remove Yii gii package for easier maintainance

[alexander-schranz]

It requires the dev-master version of yiisoft/yii-middleware but as we not using yii gii here we should better remove it and keep yii example on the stable yii middleware version.

Else we have errors like this:

Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.
Problem 1

• Root composer.json requires yiisoft/yii-gii dev-master -> satisfiable by yiisoft/yii-gii[dev-master].
• yiisoft/yii-gii dev-master requires yiisoft/yii-middleware dev-master -> found yiisoft/yii-middleware[dev-master] but it conflicts with your root composer.json require (^1.0).

Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.