Fix task group task date handlers
Fix task group task date handlers

Registering an error for task group tasks needs to remove that task
group task object from the parent task group. Otherwise the malformed
object still got used in the date calculations and caused an exception
that failed the whole block of tasks.

kr41/ggrc-core,selahssea/ggrc-core,j0gurt/ggrc-core,AleksNeStu/ggrc-core,andrei-karalionak/ggrc-core,j0gurt/ggrc-core,j0gurt/ggrc-core,plamut/ggrc-core,j0gurt/ggrc-core,selahssea/ggrc-core,VinnieJohns/ggrc-core,VinnieJohns/ggrc-core,kr41/ggrc-core,plamut/ggrc-core,josthkko/ggrc-core,edofic/ggrc-core,kr41/ggrc-core,AleksNeStu/ggrc-core,edofic/ggrc-core,VinnieJohns/ggrc-core,selahssea/ggrc-core,selahssea/ggrc-core,plamut/ggrc-core,plamut/ggrc-core,josthkko/ggrc-core,josthkko/ggrc-core,edofic/ggrc-core,VinnieJohns/ggrc-core,AleksNeStu/ggrc-core,josthkko/ggrc-core,kr41/ggrc-core,andrei-karalionak/ggrc-core,edofic/ggrc-core,andrei-karalionak/ggrc-core,andrei-karalionak/ggrc-core,AleksNeStu/ggrc-core