travisci: Remove defunct Travis CI configuration

.travis.yml

----
-language: c
-
-jobs:
-  allow_failures:
-    - os: osx
-    - stage: sanitizers
-    - arch: arm64
-  fast_finish: true
-  include:
-    - &test-linux
-      stage: test
-      os: linux
-      dist: bionic
-      arch: amd64
-      compiler: clang
-      addons:
-        apt:
-          packages:
-            - nghttp2
-            - python3-docutils
-            - python3-sphinx
-            - libunwind-dev
-            - libpcre2-dev
-      before_script:
-        - ./autogen.sh
-        - ./configure --enable-maintainer-mode --with-unwind
-      script: &script-common
-        - make -j16 check VERBOSE=1
-    - <<: *test-linux
-      arch: arm64
-    - <<: *test-linux
-      compiler: gcc
-      before_script:
-        - ./autogen.sh
-        - ./configure --enable-maintainer-mode
-    - <<: *test-linux
-      compiler: gcc
-      arch: arm64
-      before_script:
-        - ./autogen.sh
-        - ./configure --enable-maintainer-mode
-    - <<: *test-linux
-      env: WITNESS=1
-      script: make -j16 witness VERBOSE=1
-    - <<: *test-linux
-      stage: sanitizers
-      addons:
-        apt:
-          sources:
-            - sourceline: 'deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main'
-              key_url: https://apt.llvm.org/llvm-snapshot.gpg.key
-            - ubuntu-toolchain-r-test
-          packages:
-            - clang-9
-            - libunwind-dev
-            - llvm-9
-            - nghttp2
-            - python3-docutils
-            - python3-sphinx
-            - libpcre2-dev
-      env: ASAN=1 UBSAN=1
-      before_script:
-        - |
-          export ASAN_OPTIONS=abort_on_error=1,detect_odr_violation=1,detect_leaks=1,detect_stack_use_after_return=1,detect_invalid_pointer_pairs=1,handle_segv=0,handle_sigbus=0,use_sigaltstack=0,disable_coredump=0
-          export LSAN_OPTIONS=abort_on_error=1,use_sigaltstack=0,suppressions=$(pwd)/tools/lsan.suppr
-          export TSAN_OPTIONS=abort_on_error=1,halt_on_error=1,use_sigaltstack=0,suppressions=$(pwd)/tools/tsan.suppr
-          export UBSAN_OPTIONS=halt_on_error=1,print_stacktrace=1,use_sigaltstack=0,suppressions=$(pwd)/tools/ubsan.suppr
-          export CC=clang-9
-        - ./autogen.sh
-        - ./configure --enable-maintainer-mode --with-unwind --enable-debugging-symbols --disable-stack-protector --with-persistent-storage --enable-asan --enable-ubsan --enable-workspace-emulator
-    - stage: test
-      os: osx
-      osx_image: xcode12.5
-      compiler: clang
-      addons:
-        homebrew:
-          packages:
-            - docutils
-            - nghttp2
-            - sphinx-doc
-      before_script:
-        - export PATH="/usr/local/opt/sphinx-doc/bin:$PATH"
-        - ./autogen.sh
-        - ./configure --enable-maintainer-mode
-      script: *script-common
-    - <<: *test-linux
-      stage: coverity
-      env:
-        - secure: "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"
-      before_script:
-        - curl
-            --data "token=$COVTOKEN&project=varnish"
-            --insecure
-            -o coverity_tool.tgz https://scan.coverity.com/download/cxx/linux64
-        - tar xfz coverity_tool.tgz
-        - export PATH=$PATH:$(echo $(pwd)/cov-analysis-*/bin)
-      script:
-        - ./autogen.sh
-        - ./configure --enable-maintainer-mode --with-unwind
-        - cov-build --dir cov-int make
-        - tar cfz varnish.tgz cov-int
-        - curl --form token="$COVTOKEN"
-            --form email=varnish-dev@varnish-cache.org
-            --form file=@varnish.tgz
-            --form version="$TRAVIS_COMMIT"
-            --form description="$TRAVIS_BRANCH"
-            --insecure
-            'https://scan.coverity.com/builds?project=varnish'
-
-stages:
-  - name: test
-    if: type != cron
-  - name: sanitizers
-    if: type != cron AND
-        type != pull_request
-  - name: coverity
-    if: type = cron
-
-notifications:
-  irc:
-    if: branch = master AND
-        repo = varnishcache/varnish-cache
-    channels:
-      - "irc.linpro.no#varnish-hacking"
-    on_success: change
-    use_notice: true
-