Revert "Fix DEVKIT-566: as CategoryKeyProperty changes the equals behaviour, a new field will be added for the DefaultMetaDataKey"

This reverts commit 9782b57f112218a1f98998b9df39a621d7c22d8b.
Fixing DEVKIT-566, now DefaultMetaDataKey has a category as a field
removing setCategory from MetaDataKey interface
Merge pull request #6 from mulesoft/DEVKIT-566

Devkit 566