Remove old Travis CI config

.travis.yml

@@ -1,40 +0,0 @@
-sudo: false
-
-language: php
-
-php:
-  - 7.1
-  - 7.2
-  - 7.3
-  - 7.4
-  - nightly
-
-matrix:
-  allow_failures:
-    - php: nightly
-  fast_finish: true
-
-cache:
-  directories:
-    - $HOME/.composer/cache
-    - $HOME/.php-cs-fixer
-    - $HOME/.local
-
-env:
-  - AMP_DEBUG=true
-
-before_install:
-  - phpenv config-rm xdebug.ini || echo "No xdebug config."
-
-install:
-  - composer update -n --prefer-dist
-  - wget https://github.com/php-coveralls/php-coveralls/releases/download/v1.0.2/coveralls.phar
-  - chmod +x coveralls.phar
-
-script:
-  - phpdbg -qrr vendor/bin/phpunit --coverage-text --coverage-clover build/logs/clover.xml
-  - PHP_CS_FIXER_IGNORE_ENV=1 php vendor/bin/php-cs-fixer --diff --dry-run -v fix
-  - vendor/bin/psalm
-
-after_script:
-  - ./coveralls.phar