Delete units when AI is confused

[project_mercy]

If the AI's can't process its turn in a few seconds, start deleting units. If its stuck in a position where there's a carpet of units (due to poorly designed scenarios like Scramble and Renaissance), and it just sits there chunking, start deleting units until such time as it can successfully process a turn. The units don't provide anything constructive but wasted bravado for that civ, and basically shut the game down.