ARROW-7712: [CI] [Crossbow] Delete fuzzit jobs

We will focus on OSS-Fuzz, now that we have been accepted there.

Also add an OSS-Fuzz badge in the README.

Closes #6328 from pitrou/ARROW-7712-delete-fuzzit-jobs and squashes the following commits:

6c6d2c4 <Antoine Pitrou> Remove remaining fuzzit-related configuration
a6abaa9 <Antoine Pitrou> ARROW-7712:   Delete fuzzit jobs

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

Author: pitrou

README.md

@@ -21,7 +21,7 @@
 
 [![Build Status](https://ci.appveyor.com/api/projects/status/github/apache/arrow/branch/master?svg=true)](https://ci.appveyor.com/project/ApacheSoftwareFoundation/arrow/branch/master)
 [![Coverage Status](https://codecov.io/gh/apache/arrow/branch/master/graph/badge.svg)](https://codecov.io/gh/apache/arrow?branch=master)
-[![Fuzzit Status](https://app.fuzzit.dev/badge?org_id=yMxZh42xl9qy6bvg3EiJ&branch=master)](https://app.fuzzit.dev/admin/yMxZh42xl9qy6bvg3EiJ/dashboard)
+[![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/arrow.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:arrow)
 [![License](http://img.shields.io/:license-Apache%202-blue.svg)](https://github.com/apache/arrow/blob/master/LICENSE.txt)
 [![Twitter Follow](https://img.shields.io/twitter/follow/apachearrow.svg?style=social&label=Follow)](https://twitter.com/apachearrow)
 

ci/docker/linux-apt-fuzzit.dockerfile

@@ -122,8 +122,6 @@ groups:
     - test-ubuntu-18.04-r-sanitizer
     - test-debian-10-go-1.12
     - test-ubuntu-18.04-docs
-    - test-ubuntu-fuzzit-fuzzing
-    - test-ubuntu-fuzzit-regression
     - test-conda-python-2.7-pandas-latest
     - test-conda-python-2.7-pandas-master
     - test-conda-python-3.7-pandas-latest
@@ -300,9 +298,6 @@ groups:
     - test-ubuntu-18.04-r-sanitizer
     - test-debian-10-go-1.12
     - test-ubuntu-18.04-docs
-    # https://issues.apache.org/jira/browse/ARROW-7712
-    # - test-ubuntu-fuzzit-fuzzing
-    # - test-ubuntu-fuzzit-regression
     - test-conda-python-2.7-pandas-latest
     - test-conda-python-3.7-pandas-latest
     - test-conda-python-3.7-pandas-master
@@ -2058,30 +2053,6 @@ tasks:
         - docker-compose build ubuntu-docs
         - docker-compose run ubuntu-docs
 
-  test-ubuntu-fuzzit-fuzzing:
-    ci: circle
-    platform: linux
-    template: docker-tests/circle.linux.yml
-    params:
-      commands:
-        - docker-compose pull --ignore-pull-failures ubuntu-cpp
-        - docker-compose pull --ignore-pull-failures ubuntu-fuzzit
-        - docker-compose build ubuntu-cpp
-        - docker-compose build ubuntu-fuzzit
-        - docker-compose run -e FUZZIT_JOB_TYPE=fuzzing ubuntu-fuzzit
-
-  test-ubuntu-fuzzit-regression:
-    ci: circle
-    platform: linux
-    template: docker-tests/circle.linux.yml
-    params:
-      commands:
-        - docker-compose pull --ignore-pull-failures ubuntu-cpp
-        - docker-compose pull --ignore-pull-failures ubuntu-fuzzit
-        - docker-compose build ubuntu-cpp
-        - docker-compose build ubuntu-fuzzit
-        - docker-compose run -e FUZZIT_JOB_TYPE=regression ubuntu-fuzzit
-
   ############################## Integration tests ############################
 
   test-conda-python-2.7-pandas-latest:

ci/scripts/fuzzit_build.sh

@@ -951,30 +951,6 @@ services:
     command: >
       /bin/bash -c "pip install -e /arrow/dev/archery && archery lint"
 
-  ubuntu-fuzzit:
-    # Usage:
-    #   docker-compose build ubuntu-cpp
-    #   docker-compose build ubuntu-fuzzit
-    #   docker-compose run ubuntu-fuzzit
-    build:
-      context: .
-      dockerfile: ci/docker/linux-apt-fuzzit.dockerfile
-      cache_from:
-        - ${REPO}:${ARCH}-ubuntu-${UBUNTU}-fuzzit
-      args:
-        base: ${REPO}:${ARCH}-ubuntu-${UBUNTU}-cpp
-    environment:
-      <<: *ccache
-      FUZZIT_API_KEY: c0b760d37db6012fcaafd8ca5f412ba7bcd297ac969650502994b51aa11798153824442f999a067e1ef67821989ed664
-      FUZZIT_HOST: bionic-llvm7
-      CI_ARROW_SHA: ${CI_ARROW_SHA:-UNSET}
-      CI_ARROW_BRANCH: ${CI_ARROW_BRANCH:-UNSET}
-    volumes: *debian-volumes
-    command: >
-      /bin/bash -c "
-        /arrow/ci/scripts/cpp_build.sh /arrow /build &&
-        /arrow/ci/scripts/fuzzit_build.sh /arrow /build"
-
   ######################### Integration Tests #################################
 
   postgres: