Drop Travis integration (#2468)

It has been unused since Travis dropped free plans

.travis.yml

@@ -1,83 +0,0 @@
-# Two types of tests:
-#
-# 1. shell tests run using bats
-# 2. build tests also run using bats
-#
-# Shell tests are run unconditionally on Linux (see jobs.include).
-#
-# Build tests can be skipped by starting the commit message with
-# '[skip build]'.
-#
-# Build tests are run on platforms generated from all combinations
-# of keys below.
-language: c
-
-os:
-- linux
-- osx
-
-dist:
-- focal
-
-# https://docs.travis-ci.com/user/reference/osx/#macos-version
-osx_image:
-- xcode9.4.1  # macOS 10.13.6
-- xcode10.3   # macOS 10.14.4
-- xcode11.6   # macOS 10.15.7
-- xcode12.2   # macOS 10.15.7
-
-env:
-- PYTHON_BUILD_VERSION=3.9.1
-- PYTHON_BUILD_VERSION=3.7.5
-
-before_install:
-- date +%Y-%m-%dT%H:%M:%S
-
-install: git clone --depth 1 --branch v1.2.0 https://github.com/bats-core/bats-core.git bats
-
-# Default for auto-generated jobs.
-script: make test-build
-
-jobs:
-  include:
-  # Shell-based tests should execute every time.
-  - stage: test shell
-    script: make test
-    env: PYENV_NATIVE_EXT=1
-    after_script: []
-    os: linux
-  - stage: test shell
-    script: make test
-    env: PYENV_NATIVE_EXT=
-    after_script: []
-    os: linux
-
-  exclude:
-  # For each osx_image but one there should be an entry in the exclude
-  # list, to prevent duplicate Linux builds.
-  - os: linux
-    osx_image: xcode9.4
-  - os: linux
-    osx_image: xcode10
-
-  allow_failures:
-  - env: PYTHON_BUILD_VERSION=3.9.1
-
-stages:
-- test shell
-- name: test
-  if: NOT (commit_message =~ /^\[skip build\]/)
-
-# Default 
-
-notifications:
-  email:
-    on_success: never
-
-deploy:
-  provider: releases
-  api_key:
-    secure: FLWevL09KYp7V1SjJUNEdWzuomuocXwNvPr1DSAFH7mmrjKTtjzwrjINAthSqzjlDrs5B//P47l1VLyHp5byEzy673W+bOmEg8swmqc7E9FrHLRyEByd/yca3DzkZgXEXgGdY/cl7tHhM4V2fYKEgAIWbFV+takmTFMK4WkEtNg=
-  on:
-    repo: pyenv/pyenv
-    tags: true