Revert r54638 "Deprecate the $wgExtraRandompageSQL config variable by adding a hook...

Revert r54638 "Deprecate the $wgExtraRandompageSQL config variable by adding a hook, SpecialRandomBeforeSQL"
If we're going to make a generalizable plug-in point for extensions to supply their own randomization, we shouldn't be exposing it at the point of low-level database operations. The extension should instead be given the chance to pick an item any way it pleases and return a result or set of results to choose from.