Revert "[SimplifyCFG] When eliminating `unreachable` landing pads, mark `call`s as `nounwind`"

The bool is in the wrong place and might get implicitly converted from
the previous second argument - a pointer. Thinking about it more,
it's not really the best place for that functionality anyways,
only a single caller needs that.

This reverts commit 3c5b1f2d.