ci: remove Travis CI

Azure Pipelines now does everything we were doing in Travis.

And with this, we now have a single CI system!

NEWS.rst

@@ -87,7 +87,7 @@ Bug Fixes
 Changes
 -------
 
-* Windows CI transitioned to Azure Pipelines (from AppVeyor).
+* CI transitioned to Azure Pipelines (from AppVeyor and Travis CI).
 * Switched to ``pytest`` for running tests (from ``nose``).
 * Bundled zstandard library upgraded from 1.3.8 to 1.4.3.
 

README.rst

@@ -15,7 +15,7 @@ The canonical home for this project lives in a Mercurial repository run by
 the author. For convenience, that repository is frequently synchronized to
 https://github.com/indygreg/python-zstandard.
 
-|  |pipelines-status| |ci-status|
+|  |ci-status|
 
 Requirements
 ============
@@ -1598,8 +1598,5 @@ their work, consider donating some money. Any amount is appreciated.
     :target: https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=gregory%2eszorc%40gmail%2ecom&lc=US&item_name=python%2dzstandard&currency_code=USD&bn=PP%2dDonationsBF%3abtn_donate_LG%2egif%3aNonHosted
     :alt: Donate via PayPal
 
-.. |pipelines-status| image:: https://dev.azure.com/gregoryszorc/python-zstandard/_apis/build/status/indygreg.python-zstandard?branchName=master
+.. |ci-status| image:: https://dev.azure.com/gregoryszorc/python-zstandard/_apis/build/status/indygreg.python-zstandard?branchName=master
     :target: https://dev.azure.com/gregoryszorc/python-zstandard/_apis/build/status/indygreg.python-zstandard?branchName=master
-
-.. |ci-status| image:: https://travis-ci.org/indygreg/python-zstandard.svg?branch=master
-    :target: https://travis-ci.org/indygreg/python-zstandard