Stop removing functions without proving them nothrow in inlining
E.g., consider
```
struct Foo{T}; x::T; end
f(b) = fieldtype(b ? Int : Foo{Int}, 1)
```
We can conclude that f always returns `Int`. However,
we cannot remove the fieldtype call, because it throws
for `b === true`. We are a bit lucky in that our tfuncs
are currently fairly imprecise in the cases where this
would cause problems, largely masking the bug.
This is essentially a generalization of #27912. As our
tfuncs get more precise, this will get more and more
important for correctness.
