MyBatis Revert workarounds for JaCoCo issue with JDK 15

JaCoCo 0.8.6 is released.

@hazendaz , We should do this, right?

Comment From: hazendaz

All good, I'd drop jdk 13/14 though and add 16. While 13/14 are out there, bother are EOL now.

Comment From: harawata

Thank you @hazendaz for the merge and the follow up PR!