Drop obsolete/broken CI definitions

(Free) Travis-ci is gone since November 2020, cirrus seems to be
unreliable showing build breakages unrelated to changes.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

.cirrus.yml

@@ -1,23 +0,0 @@
-env:
-  CIRRUS_CLONE_DEPTH: 1
-
-freebsd_13_task:
-  freebsd_instance:
-    image: freebsd-13-0-release-amd64
-  install_script:
-    pkg install -y bison gmake pkgconf
-  build_script:
-    gmake
-  test_script:
-    gmake check
-
-linux_gcc_task:
-  container:
-    image: gcc:latest
-  install_script:
-    - apt-get update
-    - apt-get -y install bison flex
-  build_script:
-    - make
-  test_script:
-    - make check

.travis.yml

@@ -1,65 +0,0 @@
-language: c
-
-# Coverity Scan uploads
-env:
-  global:
-  # COVERITY_SCAN_TOKEN (dgibson/dtc)
-  - secure: "vlHvXe618//IM9LQaKzqsrUbjs7ng0L9UCST4kJbJnFQDXvVe5JiSmJGd4ef7mm0NUv5bMRl2W3xCiu6BYAu/NvU3tMNHoLG+JgCJs0+wLJXbWOwji/NmH7olqgJG+CmpaCMXjARF6+nrTnBYHJL6cYyf4KVoV4B0I/hLUW91+s="
-
-matrix:
-  include:
-    - addons:
-        apt:
-          packages:
-            - swig
-            - python-dev
-            - valgrind
-            - libyaml-0-2
-        coverity_scan:
-          project:
-            name: dtc
-            description: Device Tree Compiler
-          notification_email: david@gibson.dropbear.id.au
-          build_command: make
-          branch_pattern: coverity_scan
-      script:
-        - make
-        - make check && make checkm
-
-    # Check it builds properly without optional packages:
-    #     python, valgrind, libyaml
-    - script:
-        - make
-        - make check
-
-    - arch: arm64
-      addons:
-        apt_packages:
-          - swig
-          - python-dev
-          - valgrind
-          - libyaml-0-2
-      script:
-        - make
-        - make check checkm
-
-    - arch: ppc64le
-      addons:
-        apt_packages:
-          - swig
-          - python-dev
-          - libyaml-0-2
-      script:
-        - make
-        - make check
-
-    - arch: s390x
-      addons:
-        apt_packages:
-          - swig
-          - python-dev
-          - valgrind
-          - libyaml-0-2
-      script:
-        - make
-        - make check checkm