docs: Remove discussion of using Travis CI. (#21256)

These are outdated and the docker images mentioned here haven't
been updated in 4 years.

Author: waywardmonkeys

site/source/docs/compiling/Travis.rst

@@ -9,7 +9,6 @@ This section contains topics about building projects and running the output.
 - :ref:`Building-Projects` shows how to use :ref:`emccdoc` as a drop-in replacement for *gcc* in your existing project.
 - :ref:`WebAssembly` explains how Emscripten can be used to build WebAssembly files
 - :ref:`Running-html-files-with-emrun` explains how to use *emrun* to run generated HTML pages in a locally launched web server.
-- :ref:`Travis` explains how to build and test projects on Travis CI.
 - :ref:`Deploying-Pages` covers topics related to hosting Emscripten compiled web pages on a CDN.
 - :ref:`GitLab` explains how to build and test projects on GitLab.
 
@@ -21,6 +20,5 @@ This section contains topics about building projects and running the output.
    WebAssembly
    Dynamic-Linking
    Running-html-files-with-emrun
-   Travis
    Deploying-Pages
    GitLab