Cleanup irb history file in tests

This was caused by the irb spec. Note that
$HOME is set during the test setup so will
always be correct.

Library/Homebrew/test/dev-cmd/irb_spec.rb

@@ -6,6 +6,13 @@ require "cmd/shared_examples/args_parse"
 describe "brew irb" do
   it_behaves_like "parseable arguments"
 
+  describe "integration test" do
+    let(:history_file) { Pathname("#{Dir.home}/.brew_irb_history") }
+
+    after do
+      history_file.delete if history_file.exist?
+    end
+
     it "starts an interactive Homebrew shell session", :integration_test do
       setup_test_formula "testball"
 
@@ -20,5 +27,8 @@ describe "brew irb" do
         .to output(/Interactive Homebrew Shell/).to_stdout
         .and not_to_output.to_stderr
         .and be_a_success
+
+      expect(history_file).to exist
+    end
   end
 end