The short answer is "Don't worry about it". Having the JRE or SDK pre-installed is not requirement to run Tableau Server, so whatever you've already loaded on the machine is yours to manage however you wish. We essentially "don't care" what you do with the SDK
Hope that helps!
A related question: Oracle will require us to sign a maintenance agreement we use Oracle Java 8_192 or later on commercial servers in 2019.
Do we need Oracle Java on our Tableau Server?