Poncho: Simplify import failure

[dthain]

BenC pointed this out in a Parsl issue:
Parsl/parsl#3552

Basically, we are trying too hard to capture an import error and replace it with something more explanatory. (There may have been a reason for this in the past.). Now that we rely on Conda to get proper python environments everywhere, we should just import normally and (if that fails) let it fail with the normal exception.

[dthain]

Barry, can you do this one up quickly? I think it's a small change and then we can close it out...

[BarrySlyDelgado]

We now let the import errors happen by forgoing catching the exception via #3907