delete IO Type cacheKey field and use parameterType as key in PropertyIO, https://github.com/phetsims/phet-core/issues/79
delete IO Type cacheKey field and use parameterType as key in PropertyIO, https://github.com/phetsims/phet-core/issues/79

phetsims/phet-core,phetsims/phet-core,phetsims/phet-core