Completion entry details of union of methods with no call signature

Do not classify the union of methods as method if the union wouldn't contain any call signatures
Fixes #928 
Consider making this

```TypeScript
if (rootSymbolFlags & (SymbolFlags.Property | SymbolFlags.GetAccessor | SymbolFlags.SetAccessor))
```

if it's not unreasonably long.

Either that or make the other two `if`s consistent.