[2.7] adds deprecation notices.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

The `__METHOD__` constant already prefixes with `TheClass::`.

```php
namespace A;

class B
{
    public function c()
    {
        echo __METHOD__.' is deprecated.';
    }
}

$b = new B();
$b->c();
```
When I run this script, it outputs `A\B::c is deprecated.`.