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.