[morty] Revert "atf-juno: update juno-latest-oe-uboot.zip to 18.04 release"

[mrchapp]

This reverts commit 5d6fbe382083fb3384883d1d748f437f6087bbe9.

Currently, Morty only works with 17.04, as the following versions of the Juno recovery pack do not get along with the software versions as they are shipped with Morty:

• 17.07: https://lkft.validation.linaro.org/scheduler/job/299683
• 17.10: https://lkft.validation.linaro.org/scheduler/job/299656
• 18.01: https://lkft.validation.linaro.org/scheduler/job/299643
• 18.04: https://lkft.validation.linaro.org/scheduler/job/298978