Add RemoveMigrationDocBlockRector rector

[glensc]

Cleans up useless phpdoc:

-/**
- * Run the migrations.
- *
- * @return void
- */
public function up()
{
    // ...
}

-/**
- * Reverse the migrations
- *
- * @return void
- */
public function down()
{
    // ...
}

[glensc]

Please assist on:

1. will this be accepted?
2. how to name this?
3. what namespace to put the class?

Self-review:

1. the @return void can be done with other rules, so should be removed from this rector regex?

[peterfox]

I'll be honest I don't see this being an efficient use of a rector rule that we'd want to maintain. Happy to give some guidance in how you might write such a rule if you'd still want help with it.