Experiment with eliminating X11 from Petsc build

[dangunter]

https://lists.mcs.anl.gov/pipermail/petsc-users/2020-April/040728.html

Someone ran into an issue with petsc requiring the X11 lib on a Mac. From the linked (albeit old) post above, this seems like a dependency that can be controlled at configure/build time.

Is x11 currently being linked (ie is this flag already being used) and if so, does this flag work? Of course we'd need to verify that nothing broke even if the build succeeded, but hopefully 🤞 this is not a really necessary dependency.

[ksbeattie]

Motivated by #272

[ksbeattie]

The rumor is that Sandia will (eventually) be taking over idaes-ext builds.