Remove travis config

.travis.yml

----
-dist: bionic
-language: python
-python:
-  - 3.7
-sudo: required
-services:
-  - docker
-
-jobs:
-  include:
-    - stage: diff-test
-      install:
-        - pip install --upgrade pip
-        - make dev-env
-        - make lint-install
-      script:
-        - set -e
-        - if [ $(make n-docs-diff) -ne 0 ]; then make docs; fi;
-        - if [ $(make n-other-diff) -ne 0 ]; then make lint-build-test-all DARGS="--build-arg TEST_ONLY_BUILD=1"; fi;
-    - stage: push-tx
-      install:
-        - pip install --upgrade pip
-        - make dev-env
-      script:
-        - if [ $(make n-docs-diff DIFF_RANGE=$TRAVIS_COMMIT_RANGE) -ne 0 ]; then make tx-en; fi;
-    - stage: full-test
-      install:
-        - pip install --upgrade pip
-        - make dev-env
-        - make lint-install
-      script:
-        - set -e
-        - make docs
-        - make lint-build-test-all DARGS="--build-arg TEST_ONLY_BUILD=1"
-
-stages:
-  - name: diff-test
-    if: type = pull_request
-  - name: push-tx
-    if: type = push AND branch = master
-  - name: full-test
-    if: type = cron AND branch = master
-
-env:
-  global:
-    # yamllint disable-line
-    secure: 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