mtlb_sparse() no longer exists

Reported by Samuel GOUGEON (@sgougeon)

BUG DESCRIPTION:
----------------
From the example given in help mtlb_sparse:

--> X=sparse(rand(2,2)); Y=mtlb_sparse(X);

Undefined variable: mtlb_sparse


ERROR LOG:
----------
Undefined variable: mtlb_sparse


HOW TO REPRODUCE THE BUG:
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X = sparse(rand(2,2));
Y = mtlb_sparse(X);