Remove the legacy package list for install path overrides

[roborourke]

The legacy list was for Composer v1 and the transition between the 2. I think we can ditch this to avoid errors in future where packages are unintentionally forced into the vendor directory.

Fixes #839

[roborourke]

The tests seem to consistently fail on ES connectivity. Maybe there's some new general issues with local server on travis there to look into.

[mikelittle]

Came to look at the failing tests and they are passing now.