[nancy] Remove grelon cluster and and sys contact to site

data/grid5000/sites/nancy/clusters/grelon/grelon.json

.../grid5000/sites/nancy/clusters/grelon/nodes/grelon-1.json

...grid5000/sites/nancy/clusters/grelon/nodes/grelon-10.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-100.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-101.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-102.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-103.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-104.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-105.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-106.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-107.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-108.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-109.json

...grid5000/sites/nancy/clusters/grelon/nodes/grelon-11.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-110.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-111.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-112.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-113.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-114.json

...rid5000/sites/nancy/clusters/grelon/nodes/grelon-115.json