A down() equivalent to foreignIdFor()

[LuanHimmlisch]

Very straight forward I think. A drop counter-part of the foreignIdFor method for migrations.

It would drop the column generated from a foreignIdFor without a column name parameter.

public function down()
{
    Schema::table('examples', function (Blueprint $table) {
        $table->dropForeignIdFor(SomeModel::class);
    });
}