This is not violent language. This is a generic well known English idiom with a known meaning, in this case a positive one. In fact you can search Google for "define killer" and one of the dictionary definitions that comes up is:

very impressive or effective; excellent.

In fact this is the first definition for the work as used grammatically here. You seem to be conflating the noun "killer" with the adjective form for which the first most common definition is positive:

https://www.merriam-webster.com/dictionary/killer

The replacement suggested here is nonsensical and does not convey the same meaning. There is no reason for this change, in the context of software a "killer feature" is well understood and has no relation to violence.