Revert "Add yarn 1.9.2, remove yarn 1.7.0"
Revert "Add yarn 1.9.2, remove yarn 1.7.0"

This reverts commit 53d2e79bcaedabb88d1107de4deaa4bba5e899ae.

- This version of yarn broke tests. Reverting for now for cflinuxfs3
release

[#159368358]

cloudfoundry/nodejs-buildpack,cloudfoundry/nodejs-buildpack,cloudfoundry/nodejs-buildpack,cloudfoundry/nodejs-buildpack