AI prototype chain cleanup.

Use prototype = Object.create(parent) instead of prototype = new parent(...) to avoid calling the constructor needlessly (as it is redundant with the base constructor call in the constructor calls the parent constructor).

Testfile reference comes from rP7259,
"initial terrible AI player scripts" had it since rP8891,
jubot copied it since rP9378,
qbot copied it since rP10654
qbot-wc (later aegis) copied it since rP12267,
aegis copied it since rP13683,
petra copied it since rP14865.

rP14582 used Object.create correctly for new code in aegis that was adopted for petra too in rP14865.

Differential Revision: https://code.wildfiregames.com/D2238
Patch By: Krinkle