`remove_assertions` changes return value when used in a call expression

[sircfenner]

For example, applying remove_assertions with the default parameter for the rule, the following input:

local head = assert(character:FindFirstChild("Head"), "head is missing!")

becomes:

local head = character:FindFirstChild("Head") and nil

This changes runtime behavior in an unexpected way, because head is always nil even when the character does have a child named Head. Expected output is:

local head = character:FindFirstChild("Head")

---

When preserve_aguments_side_effects is set to false, the output is:

local head = nil

Not sure if this is intended either. I think whether the return value is used (so, whether the assert is an expression or a statement?) should probably be factored in here.

Tested on version 0.13.0.