Remove all uses of system calls

[joshcarp]

for the sake of reusability and reliability it would greatly simplify this project if we removed all uses of os.exec calls:

1. In sysl modules
2. getting the git remote:

   sysl-catalog/pkg/catalog/spec.go

   Line 33 in 462aa87

   cmd := exec.Command("git", "config", "--get", "remote.origin.url")

This means that it can more reliably run in different environments (wasm/docker).
As for the lost functionality; I think the current solutions are bandaids and there are more robust ways of getting the same functionality