change log of prune when nothing is found to debug visibility

[Makio64]

Currently the prune is used internally in many functions and it 'spam' the log especially when No unused properties found :

for example :

resample: 0.83ms
prune: Removed types... Node (29)
flatten: 1.13ms
prune: No unused properties found.
weldVertices: 8.36ms
prune: No unused properties found.
prune: No unused properties found.
simplifyMesh: 11.40ms
//etc...

after this change :

resample: 0.83ms
prune: Removed types... Node (29)
flatten: 1.13ms
weldVertices: 8.36ms
simplifyMesh: 11.40ms
//etc...