Remove composer-locator

[jspaetzel]

Because this contains a plugin it prompts on every composer execution,

mindplay/composer-locator contains a Composer plugin which is currently not in your allow-plugins config. See https://getcomposer.org/allow-plugins
Do you trust "mindplay/composer-locator" to execute code and wish to enable it now? (writes "allow-plugins" to composer.json) [y,n,d,?]

rather than enable the plugin, why not just remove this since it's so sparsely used?

I've also bundled in a "minimum-stability": "dev" change here because I don't see any reason why this would need a minimum stability of dev. Old artifact maybe?

[rvanlaak]

As long as tests pass there is no need for minimum stability, as this is a Composer root tag (so only applies on the root level of a project requiring this package).

Thanks for the PR!