Discontinue recursive check for the boxfile

[glinton]

trafficstars

Currently, we check up the directory tree for a boxfile.yml and use that if found. This seems to be more dangerous than helpful now that we check for the boxfile and validate it in separate steps. One thing we need to retain awareness for, as far as parent apps go, is warn that apps in subdirectories of an already 'exported' app are not supported.