Drop additional check

This forces the `require yq` to only happen at the start of the
top-level functions which makes more sense and is easier to manage.

Closes https://git.autonomic.zone/coop-cloud/abra/issues/183.

abra

@@ -498,7 +498,6 @@ require_docker_version() {
 }
 
 require_valid_yaml() {
-  require_yq
   $YQ e "$1" > /dev/null || error "Invalid YAML '$1'"
 }