assessmentInitialize is not a valid hook for assessment config rb file but is included in default rb file

[20wildmanj]

Currently, the default assessment template (lib/__defaultAssessment.rb) includes a method assessmentInitialize as follows:

def assessmentInitialize(course)
    super("##NAME_LOWER##",course)
    @problems = []
  end

This implies that an instructor can define problems via this hook by modifying the config rb file. However assessmentInitialize has been deprecated for years, and is not called during assessment creation, but the code still exists, along with installProblems, which was used to install the problems defined by assessmentInitialize. This code is all deprecated since importing uses the config yml file as the source of truth. The default assessment config file and the assessmentInitialize and installProblems code should be removed to prevent confusion.

In a similar vein, the course config file should also be updated to not include gradebookMessage as it is also not a valid hook.

[damianhxy]

Related to #1926