Remove legacy add_negative_message_expectation method
requested to merge github/fork/mrageh/remove-negative-message-expectation-from-nil-proxy into master
Created by: mrageh
In the past this method was used to negate expectations, but since [1] it's not been used. Therefore this commit removes it.
1.) https://github.com/rspec/rspec-mocks/commit/9357e4de76838157c8ea7d4a4ad6d0ae11882b22