mod/hotpot do not require grade record for HotPot reports
mod/hotpot remove hotpot grade from gradebook if not required; remove grade filter and column from hotpot reports if not required
mod/hotpot remove unecessary HotPot grade items
mod/hotpot small optimaization to code that calculates grades for all hotpots
mod/hotpot fix hotpot_update_grades() is not defined message from hotpot upgrade script