formats: stylistic change of module references
formats: stylistic change of module references

in-line with the rest of the module and coding style make changes to:
* refer to the schema module by its bound name SCHEMA
* not refer to methods from this module by their full namespace

Signed-off-by: Joshua Lock <edc229f50a11a11cdece0270af6320fb299dca1e@vmware.com>

secure-systems-lab/securesystemslib,secure-systems-lab/securesystemslib