Add `erase_old_module_code` function to do just that during upgrade

[pbchase]

Add function, erase_old_module_code, to
upgrade.py to erase old module versions from a target directory.

Call this new function with a target directory of env.upload_target_backup_dir

redcap_deployment/upgrade.py

Line 28 in 602cb1d

online()

[pbchase]

@ChemiKyle @tlstoffs can we safely do this by erasing all but the latest version? Such a plan is a bit ham-handed, but it is easy. The question is, do we need to support the presence of module code that is more modern than the activated version?

If not, we will need to read the activated versions from the database to know when to preserve an older version. I want to be lazy, but I fear we need to "do the right thing"