CI: Only post Appveyor IRC notifications when the build fails

Implements 27275.

.appveyor.yml

@@ -54,9 +54,6 @@ test_script:
             Execute-Bash "VERBOSE=1 make -j2 check"
     }
 
-on_success:
-- cmd: C:\Python27\python.exe %APPVEYOR_BUILD_FOLDER%\scripts\test\appveyor-irc-notify.py irc.oftc.net:6697 tor-ci success
-
 on_failure:
 - cmd: C:\Python27\python.exe %APPVEYOR_BUILD_FOLDER%\scripts\test\appveyor-irc-notify.py irc.oftc.net:6697 tor-ci failure
 

changes/ticket27275

@@ -0,0 +1,3 @@
+  o Minor features (continuous integration):
+    - Only post Appveyor IRC notifications when the build fails.
+      Implements ticket 27275.