MDL-69308 upgrade: remove all the < 3.6.0 upgrade steps
This just deletes all the upgrade steps previous to 3.6.0. Some small adjustments, like tweaking globals can also be applied when needed. Also includes an upgrade step to prevent upgrading from any version < 2018120300 (v3.6.0) as anti-cheating measure. Note that in this case, there wasn't any case of upgradelib functions being used, hence we haven't to deprecate/remove anything in codebase. When there is such a need, that is done in separate commits (one for each function) and documented here. See MDL-65809 commits for an example removing/deprecating a good number of functions.