ci: looks like we don't need to set BUNDLER_GEMFILE anymore

previously we had to because of these bugs:

bundler:
- rubygems/bundler#6162
- rubygems/bundler#6154

cruby docker:
- docker-library/ruby#209
- docker-library/ruby#306

jruby docker:
- jruby/docker-jruby#65
- https://github.com/cpuguy83/docker-jruby/pull/67/files

concourse/tasks/gem-test/gem-build-java.sh

@@ -13,7 +13,6 @@ OUTPUT_DIR="../gems"
 # cleanup, see extconf.rb do_clean
 mkdir -p .git
 
-export BUNDLE_GEMFILE="$(pwd)/Gemfile"
 bundle install --local || bundle install
 
 # generate a fake version number

concourse/tasks/gem-test/gem-build.sh

@@ -19,7 +19,6 @@ OUTPUT_DIR="../gems"
 # cleanup, see extconf.rb do_clean
 mkdir -p .git
 
-export BUNDLE_GEMFILE="$(pwd)/Gemfile"
 bundle install --local || bundle install
 
 # generate a fake version number

concourse/tasks/gem-test/gem-install-and-test.sh

@@ -16,7 +16,6 @@ popd
 
 pushd nokogiri
 
-  export BUNDLE_GEMFILE="$(pwd)/Gemfile"
   export BUNDLE_CACHE_PATH="${BUNDLE_APP_CONFIG}/cache"
   bundle -v
   bundle config

concourse/tasks/rake-test/run.sh

@@ -35,12 +35,6 @@ pushd nokogiri
 
   test_task="test"
 
-  # omg, jruby docker maintainers.
-  # see https://github.com/rubygems/bundler/issues/6162
-  # see https://github.com/rubygems/bundler/issues/6154
-  # and see https://github.com/docker-library/ruby/pull/209 which was the fix for cruby docker images.
-  export BUNDLE_GEMFILE="$(pwd)/Gemfile"
-
   bundle install --local || bundle install
   bundle exec rake generate # do this before setting frozen string option, because racc isn't compatible with frozen string literals yet