XPManager lets you change the amount of experience delivered by monsters or by mining ores or even breaking blocks
It's really easy to use you only need to modify the config.yml file and then reload in order for the plugin to acknowledge the changes
Code (YAML):
Entity:
SKELETON:
type
: ADDITION
value
: 0
You can change the type of XP modification from ADDITION / MULTIPLICATION / REPLACEMENT
You will find all entity types and types of block in the configuration file