Fix Stream#file? duplicates. And the spec

lib/gitlab/ci/trace/stream.rb

@@ -25,10 +25,6 @@ module Gitlab
           self.path.present?
         end
 
-        def file?
-          self.path
-        end
-
         def path
           self.stream.path if self.stream.respond_to?(:path)
         end

spec/lib/gitlab/ci/trace/stream_spec.rb

@@ -17,7 +17,6 @@ describe Gitlab::Ci::Trace::Stream, :clean_gitlab_redis_cache do
     it { is_expected.to delegate_method(:path).to(:stream) }
     it { is_expected.to delegate_method(:truncate).to(:stream) }
     it { is_expected.to delegate_method(:valid?).to(:stream).as(:present?) }
-    it { is_expected.to delegate_method(:file?).to(:path).as(:present?) }
   end
 
   describe '#limit' do