Cody tidy in CRM_Core_State

[braders]

Overview

This tidies CRM_Core_State in 3 ways:

• Documents the $page params as CRM_Core_Form rather than CRM_Core_Page. This is required as CRM_Core_Page does not extend HTML_QuickForm_Page and so does not have the necessary handle method.
• Removes the getNextState class. This has not been used in CiviCRM core for at least 9 years, and cannot work correctly as $page is undefined.
• Removes the debugPrint method. This is not used in CiviCRM core and would be unlikely to work correctly as CRM_Core_State would not be castable to a string (i.e. _next and _back).

Before

Various code quality issues.

After

Fewer code quality issues in CRM_Core_State.

[civibot]

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