Revert "Standardize the entry-point for Julia execution (#50974)"

[lgoettgens]

This reverts commit 8e14322.

As proposed by @Seelengrab in #50974 (comment).

This is not meant to be a permanent revert of #50974, but a possibility to have working PkgEval and nightly testing for packages (https://github.com/julia-actions/julia-buildpkg @latest doesn't work with it) until a solution to the discussion there has been decided on.

[vtjnash]

As far as I can tell from the current discussion, this is our best current option. It avoid making the final decision on what API will be used unnecessarily stressful in the short-term, allows people to voice their opinions, and then possibly we will still just re-land this PR by the end of the week, if that is the decision. @Keno

[Keno]

Per discussion earlier today, this is accepted for the time being, with apologies to the people who already updated their scripts and a goal to get this brought back in the next few days with one of the options to smooth the transition.