Revert "[CodeGenPrepare] Fix isIVIncrement (PR49466)"

This reverts commit cf82700a due to a compile timeout when building the following with `clang -O2`:

```
template <class, class = int> class a;
struct b {
  using d = int *;
};
struct e {
  using f = b::d;
};
class g {
public:
  e::f h;
  e::f i;
};
template <class, class> class a : g {
public:
  long j() const { return i - h; }
  long operator[](long) const noexcept;
};
template <class c, class k> long a<c, k>::operator[](long l) const noexcept {
  return h[l];
}
template <typename m, typename n> int fn1(m, n, const char *);
int o, p;
class D {
  void q(const a<long> &);
  long r;
};
void D::q(const a<long> &l) {
  int s;
  if (l[0])
    for (; l.j(); ++s) {
      if (l[s])
        while (fn1(o, 0, ""))
          ;
      r = l[s] / p;
    }
}
```