Revert "[clang][CodeGen] Emit annotations for function declarations."

This reverts commit c6a33ff4. Makes
clang segfault.

// clang t.cc
class a;
class c {
 public:
  [[clang::annotate("")]] c(const c *) {}
};
class d {
  d(const c *, a *, a *);
  c e;
};
d::d(const c *f, a *, a *) : e(f) {}