Remove Composer dev dependencies from package output

[arithmetric]

When a Composer based build is packaged, development dependencies in composer.json should be excluded from the vendor resources included in the package output.

Follow up from #284.

[jhedstrom]

We should also regenerate the autoload files so they don't include the dev dependencies. This may be automatically done depending on how we remove them (otherwise composer dump-autoload --no-dev would do it).

[grayside]

If we end up running dump-autoload for a package, should we also run with --optimize?

This still leads to pushing the dev dependencies, I found composer remove --update-no-dev as a possibility, though I haven't tested to see if that's frustratingly slow.

[jhedstrom]

In manual testing, running composer install --no-dev works, and is super fast. We could run this after packaging so as not to change the local install.

[jhedstrom]

This is merged now.