SessionsController+spec don't access session data.

Not directly, anyway; they call up to methods in ApplicationController
for the current user or the current user's ID (actually slug).

RSpec: 906 examples, 0 failures
RuboCop: 229 files inspected, no offenses detected
Minor spec cleanup.

Had accidentally checked in a couple of RSpec focus-aliased specs.
What's an "RSpec focus-aliased spec"? See the doc at
https://www.relishapp.com/rspec/rspec-core/v/3-1/docs/example-groups/ali
asing

RSpec: 906 examples, 0 failures
RuboCop: 229 files inspected, no offenses detected