Fix part of #7450: Modify private methods in UserLastExplorationActivityOneOffJobTests (#7824)
Fix part of #7450: Modify private methods in UserLastExplorationActivityOneOffJobTests (#7824)

* Changed private method calls to pulic method calls.

* Changed private method calls to public method calls

* Changed private method calls to public method calls

* Changed private method calls to public method calls

oppia/oppia,brianrodri/oppia,prasanna08/oppia,brianrodri/oppia,oppia/oppia,kevinlee12/oppia,oppia/oppia,prasanna08/oppia,brianrodri/oppia,oppia/oppia,brianrodri/oppia,prasanna08/oppia,kevinlee12/oppia,prasanna08/oppia,oppia/oppia,prasanna08/oppia,kevinlee12/oppia,brianrodri/oppia,kevinlee12/oppia,kevinlee12/oppia