Multiple external repo docs are not up to date

[phackstock]

legacy-definitions is not defined here:

nomenclature/docs/user_guide/config.rst

Lines 47 to 58 in 1a2c2ed

	repositories:
	common-definitions:
	url: https://github.com/IAMconsortium/common-definitions.git/
	definitions:
	region:
	repository: common-definitions
	variable:
	repositories:
	- common-definitions
	- legacy-definitions
	mappings:
	repository: common-definitions