remove test_pr.py

This was the last item to address in resolving  #7127, where it was
deemed that there isn't much value in keeping this around.

CONTRIBUTING.md

@@ -1,45 +1,45 b''
 ## Opening an Issue
 
 When opening a new Issue, please take the following steps:
 
 1. Search GitHub and/or Google for your issue to avoid duplicate reports.
    Keyword searches for your error messages are most helpful.
 2. If possible, try updating to master and reproducing your issue,
    because we may have already fixed it.
 3. Try to include a minimal reproducible test case
 4. Include relevant system information.  Start with the output of:
 
         python -c "import IPython; print(IPython.sys_info())"
 
    And include any relevant package versions, depending on the issue,
    such as matplotlib, numpy, Qt, Qt bindings (PyQt/PySide), tornado, web browser, etc.
 
 ## Pull Requests
 
 Some guidelines on contributing to IPython:
 
 * All work is submitted via Pull Requests.
 * Pull Requests can be submitted as soon as there is code worth discussing.
   Pull Requests track the branch, so you can continue to work after the PR is submitted.
   Review and discussion can begin well before the work is complete,
   and the more discussion the better.
   The worst case is that the PR is closed.
 * Pull Requests should generally be made against master
 * Pull Requests should be tested, if feasible:
     - bugfixes should include regression tests
     - new behavior should at least get minimal exercise
 * New features and backwards-incompatible changes should be documented by adding
   a new file to the [pr](docs/source/whatsnew/pr) directory, see [the README.md
   there](docs/source/whatsnew/pr/README.md) for details.
 * Don't make 'cleanup' pull requests just to change code style.
   We don't follow any style guide strictly, and we consider formatting changes
   unnecessary noise.
   If you're making functional changes, you can clean up the specific pieces of
   code you're working on.
 
-[Travis](http://travis-ci.org/#!/ipython/ipython) does a pretty good job testing IPython and Pull Requests,
-but it may make sense to manually perform tests (possibly with our `test_pr` script),
+[Travis](http://travis-ci.org/#!/ipython/ipython) does a pretty good job testing
+IPython and Pull Requests, but it may make sense to manually perform tests,
 particularly for PRs that affect `IPython.parallel` or Windows.
 
 For more detailed information, see our [GitHub Workflow](https://github.com/ipython/ipython/wiki/Dev:-GitHub-workflow).