Remove unused ExpectationList#match_but_out_of_order

This was added in this commit [1] as part of #633, but was never used. I
suspect it was accidentally left over after I changed my mind and added
the optional `ignoring_order` keyword argument to
`ExpectationList#match`.

[1]: 0800c6f

lib/mocha/expectation_list.rb

@@ -21,10 +21,6 @@ def match(invocation, ignoring_order: false)
       matching_expectations(invocation, ignoring_order: ignoring_order).first
     end
 
-    def match_but_out_of_order(invocation)
-      matching_expectations(invocation).first
-    end
-
     def match_allowing_invocation(invocation)
       matching_expectations(invocation).detect(&:invocations_allowed?)
     end