Clean up nightlies to turn off Epetra

[ikalash]

Also remove duplicate builds (e.g., if there is a non-Epetra and Epetra build on a machine, the Epetra one should be removed).

[mperego]

@ikalash @jewatkins, thanks to this PR: trilinos/Trilinos#12869, Trilinos_ENABLE_Epetra=OFF is no longer needed to turn off Epetra, as it is now off by default and not turned on by packages like Thyra.

[ikalash]

Good to know. I already turned off Epetra in most of the builds. Speaking of which, do we want to turn off Epetra in the spack nightly as well? I assume we do.

[mperego]

Yes, thanks! We can remove the epetra flag for spack builds as well.

[ikalash]

I just checked and the spack build already has Epetra off in Trilinos by default. Closing.