Revert "Add .gitlab-ci.yml"

This reverts commit e113e7d7.
4 jobs for master in 3 minutes and 3 seconds
Status Job ID Name Coverage
  Build
passed #1412781
build

00:00:40

 
  Test
passed #1412783
codequality

00:00:56

failed #1412782
test

00:02:22

 
  Production
skipped #1412784
production
 
Name Stage Failure
failed
test Test There is an unknown failure, please try again
Cloning into '/builds/shinya/minimal-ruby-app'...
Checking out fc666473 as master...
Skipping Git submodules setup
$ # Auto DevOps variables and functions # collapsed multi-line command
$ setup_test_db
$ cp -R . /tmp/app
$ /bin/herokuish buildpack test
-----> Unable to select a buildpack
ERROR: Job failed: exit code 1