This function takes a Git owner / repo and list of functions.
The function queries the functions for the owner using the list-functions function - parses the result and then reconciles the differences by deleting any functions which are not in the deployment list but that also match the repo.
Event: initial push
owner: alexellis repo: alexa-skill functions: fn1, fn2
Event: second push with fn2 removed
owner: alexellis repo: alexa-skill functions: fn1
fn2 is now orphaned so the garbage-collect will remove it.
Event: third push with fn1 renamed to fn3
owner: alexellis repo: alexa-skill functions: fn3
fn1 is now orphaned so will be deleted