Remove deprecated "job as class" format

[odinserj]

If you are using only expression trees syntax (Enqueue(() => Console.WriteLine)), this issue is not for you.

"Job as class" format was introduced in version 0.1 and became obsolete in 0.6 (replaced with expression trees syntax). Version 0.7 banned to create jobs in this deprecated format, but still processes them.

Main problems – differences in argument storage structure and in performance methods. It makes difficult to make some things (#62, #80, etc.), takes more time to write unit tests and requires more testing.

There is a way for very few users to upgrade jobs through sitting on 0.7 before processing the last old job, so the support will be removed in 0.8 completely.