Remove direct link to CRDCH schema

[gaurav]

In the head_and_mouth/test_load.py, we download the CRDCH schema in YAML directly from GitHub:

example-data/head-and-mouth/test_load.py

Lines 13 to 14 in a5de29d

	# The URI where the CRDCH YAML file is located.
	CRDCH_YAML_URI = 'https://raw.githubusercontent.com/cancerDHC/ccdhmodel/v1.1/model/schema/crdch_model.yaml'

Instead, we should store the CRDCH schema in the crdch_model file (cancerDHC/ccdhmodel#162).