A little clean for Skill Damage Adjustment

* re-Disabled the ADJUST_SKILL_DAMAGE by default (core.h) that enabled by accident since 794c1a8. :P
* Removed MAX_MAP_SKILL_MODIFIER variable.
* Removed fixed array for skill damage adjustment in each map.

Signed-off-by: Cydh Ramdh <house.bad@gmail.com>