Should strip this annotation

Output:
```
class A {
  a: Function;
  a() {}
}
```
Output:
```
class A {
  a: Function;

  a() {}
}
```
It should strip the `a: Function;` line.  If you compile the code with flow, that line gets stripped out of the output, but if you compile it with TypeScript, it acts as a duplicate declaration which overrides the original, resulting in code where `a` is `undefined`.