`u <= (u <= (unsigned)b)` can be folded into `(u <= (unsigned)b)`

Consider the following test case which is taken from https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119422.
https://godbolt.org/z/feoGYh15d
https://alive2.llvm.org/ce/z/AjmXuN
```cpp
int src(unsigned u, bool b)
{
  return u <= (u <= (unsigned)b);
}

int tgt(unsigned u, bool b)
{
  return u <= (unsigned)b;
}
```