Revert "Pulls random tankbot spawns.  There was much rejoicing."

This reverts commit eb29f38eb6c0551371459be088ede218ab5c3f4a.

Reinstates tankbot spawn.

I'm disabling the cannon against folks on foot.
Ensures that the tankbot is awful hesitant to use its primary: you've got to be in range and sufficently large or Friendly to get the 120mm as an option.