Is it possible to remove Emergency call feature on the lock screen?
Unfortunately there is no way to do this in native iOS (without a jailbreak).

The emergency call option is available with both the simple and complex passcode. 

I assume the goal is that it would allow anyone to make an emergency call even if they don't know or forgot the passcode, and as a result could be an important safety feature.

The only way to disable it is to turn off the passcode - something with obvious undesirable effects.