ICU-20482 Remove Travis CI Doxygen build.

.travis.yml

@@ -1,28 +1,6 @@
 matrix:
   include:
 
-    # ICU4C Docs Build
-    #    TODO: publish the latest built docs from master on GitHub pages.
-    #          See https://gist.github.com/vidavidorra/548ffbcdae99d752da02 for ideas.
-    - name:     "c: docs"
-      dist:     xenial
-      language: cpp
-      addons:
-         apt:
-           update: true
-           packages:
-             - doxygen
-      before_script:
-        - cd icu4c/source
-        - ./runConfigureICU Linux --disable-renaming
-      script:
-        # fail if 'warning:' appears in doxygen's output, but ignore warnings from file Doxyfile.
-        # The Doxygen version from Travis is down-rev, and doesn't recognize some options
-        # in the Doxyfile config file.
-        # Regex note: (?! ... ) is a negative lookahead. Succeed if the pattern is not present.
-        - set +o pipefail && make doc 2>&1 | tee doxygen.log && ( ! grep -P 'warning:(?! .* file Doxyfile)' doxygen.log )
-
-
     - name: "j"
       language: java
       env:      BUILD=ICU4J