Preparing the data file
=======================

The data file is named after the Moodle branch, for example:
not_in_MOODLE_310_STABLE, and contains all files present in previous Moodle
versions for which a direct upgrade to that version is possible from.  So for
for Moodle 3.10, it's Moodle 3.5 or later as listed under
https://docs.moodle.org/dev/Moodle_3.10_release_notes#Server_requirements.

This data file is generated by the corresponding diff_prepare-MAJORVERSION
script.  The files checked by upgrade_stale_php_files_present() must be
removed manually.