Random-map-script cleanup.

Move duplicate code of the area- and object-group placing methods to retryPlacing and two coordinate-randomization functions.
Remove three unused functions (println obsolete since r9096, chooseRand and its helper argsToArray since before r6391).
Inline local calls to GetMapSize() and IsCircularMap(). Keep unused isCircularMap for API access. Cache variables when retrying.
Map-generation can finish 2% faster.