Remove unnecessary preparation checks.

This was originally included to do something during preparation and potentially catch an invalid environment before doing things like fetching files. In reality this doesn't work as expected since the environment for jacamar (even downscoped) is not a full user environment. This means that on a number of instance we may not have loaded the scheduler at the time the application will check (it might only happen after we created and pipe the related command). Removing this just avoid awkward configurations that are currently required to address a workflow that doesn't provide immediate value.

Final, note we don't leverage either Prepare or Cleanup at the executor level since everything that matters is correctly managed across all instances. If we need to add this in the future I'm good but since there is not clear immediate need I've gone ahead and removed all related code/tests.

Closes #66 (closed)