This assignment is only used by the Projects::NetworkController, so
we're needlessly assigning this very generically-named instance variable
on every controller which includes `ExtractsPath`, which is quite a few.

Further, the way we were passing this hash to
`HashWithIndifferentAccess` caused the following deprecation warning
after upgrading to Rails 5:

    DEPRECATION WARNING: #to_hash unexpectedly ignores parameter
    filtering, and will change to enforce it in Rails 5.1. Enable
    `raise_on_unfiltered_parameters` to respect parameter filtering,
    which is the default in new applications. For the existing
    deprecated behaviour, call #to_unsafe_h instead. (called from new at
    lib/extracts_path.rb:116)