travis: Remove Travis CI

.travis.yml

@@ -1,23 +0,0 @@
-language: cpp
-dist: xenial
-
-addons:
-  apt:
-    sources:
-      - ubuntu-toolchain-r-test
-    packages:
-      - python3-pip
-      - python3-setuptools
-      - ninja-build
-      - gcc-7
-
-install:
-  # The meson included in the Xenial repositories is too old (0.29).
-  - pip3 install meson
-  - export CC=gcc-7
-
-script:
-  - mkdir build
-  - meson build
-  - ninja -v -C build
-  - meson test -v -C build