Eloy Lafuente authored Jun 14, 2017 and Dan Poltawski committed Jul 10, 2017

This just deletes all the upgrade steps previous to 3.0.0. Some
small adjustments, like adding missing MOODLE_INTERNAL or tweaking
globals can also be applied when needed.

Also includes an upgrade step to prevent upgrading from any
version < 2015111600 (v3.0.0) as anti-cheating measure.

Next commit will get rid of/deprecate all the upgradelib functions
not used anymore in codebase.