The easiest way to remove such plantlets from Microsorum (javafern) is usually to just gently scratching them off, using your fingernails. This will do minimal harm to the original leaf and secure that the plantlet keep the tiny rhizome, where roots are dangling from. In this way you can keep the leaves on original plant and have fully functional offspring. The latter can be placed somewhere else, to grow new plants or given away to fellow aquarists.
Personally I too find these plantlets do not contribute to the good look of a Microsorum in a planted tank.
The growth of many plantlets on a leaf of Microsorum is often a sign of this leaf (or sometimes entire plant) being stressed - this is not allways the case, though! Detached leaves of Microsorum often produce an abundance of offspring, if left floating around in the tank, before they finally decompose.