Delete `.travis.yml` because this repo uses GitHub Actions instead (#2030)

https://app.travis-ci.com/github/espeak-ng has no record of CI runs.

.travis.yml

@@ -1,18 +0,0 @@
-language: c
-compiler:
-  - gcc
-  - clang
-
-branches:
-  only:
-    - master
-
-before_install:
-  - sudo apt-get update -qq
-  - sudo apt-get install -qq libpulse-dev portaudio19-dev libsonic-dev
-
-script:
-  - ./autogen.sh
-  - ./configure
-  - make
-  - make check