Remove starter implementations for exercises with positions 21 or greater

[stkent]

Ref.: https://github.com/exercism/xjava/blob/master/POLICIES.md#starter-implementations

[redshirt4]

Are the exercise positions (>= 21) referring to this ordered list? http://exercism.io/languages/java/exercises

[Smarticles101]

No, they refer to the config file. @redshirt4

[stkent]

(Those two lists are generally in sync; the website might lag behind the config file by a few days is all :))

[Smarticles101]

Lol yeah I just realized that the site follows the order in the config file.

[Smarticles101]

Closed by #681