In the context of discussion about mergers and acquisitions, I believe "killing a competitor" almost exclusively means purchasing a company so that it's no longer a threat. In the course of doing so, you assimilate the acquiree's users, or at least try to. This is the meaning I interpreted from the comment you responded to.

The rarer definition, which is that a company actually shuts down the product and doesn't make an attempt to migrate its users, strikes me as something more typical for a small startup that has not yet reached real market validation, but which has very impressive R&D.