Require 'commit' argument in custom script run() method

[jeremystretch]

Proposed Changes

#4262 introduced support for an optional commit argument in a custom script's run() method. This issue serves to document the deprecation of this as an optional argument: Beginning with v2.10, a custom script's run() method must accept a commit argument.

Justification

Removes superfluous backward-compatibility logic from core. A custom script doesn't necessarily need to do anything with the commit argument; it just needs to accept it when called via run_script().