Remove cakephp/plugin-installer dependency

[othercorey]

Can we remove this dependency? Does any code in debug_kit need it?

[ADmad]

It doesn't, unless debugkit is doing something special.

The plugin installer readme states:

Your plugins themselves do not need to require cakephp/plugin-installer

[dereuromark]

The app has it
https://github.com/cakephp/app/blob/master/composer.json#L11

Technically, it is a bit cleaner to have the dependency on the plugins, thus auto requiring it from the app perspective.
But I can see that this is a bit annoying to do for all plugins.
So app only seems fine.