First you may want to note that this usage of "ablegen" isn't very common. As a native speaker, I actually had to check whether you may have meant "anlegen". A more common or contemporary version of the sentence would be
Natürlich legt er es nicht im geringsten darauf an, den Herrn von Prackwitz zu ruinieren.
The example sentence that DWDS quotes is from a novel by Hans Fallada that was published in 1953.
As Torsten Link already said, "es auf etwas anlegen" is a fixed phrase. I haven't looked into it for this answer, but I'd assume it originated with some kind of weapon that you aim or train at something or somebody ("Ich lege es (die Waffe) auf etwas / jemanden an"). In this case, "es" would refer to the weapon, which isn't actually there anymore in the figurative use of the phrase.
"ablegen" is commonly used literally, as for example in
Ich lege das Paket ab, denn es zu schwer für mich.
I put the package down, because it is to heavy for me.
or figuratively, for example with (bad) habits
Ich versuche schon lange, das Rauchen abzulegen.
I have been trying for a long time to quit smoking ("to put smoking down").
A usage that's also a bit fusty is to use "ablegen" in connection with coats, jackets or the like
Möchten Sie nicht ablegen?
Wouldn't you like to take off your coat?