CRM-10164

cleaned up code, and checked for proper execution of various conditions defined in preproccess.

removed un-used variables initialization, shortened the code at some places maintaning same logic.

the variables mentioned in issue description which are in question does the following:
  - _participantId : used in waitlist concept
  - _participantIDS : used in Confirmation form postprocess / line items processing
  - registerById : used for updating primary participant info.

so didn't tried to temper them