Following T325977, which has enabled Investigate by default (changing the default value of wgCheckUserEnableSpecialInvestigate to true from false), the explicit definition of wgCheckUserEnableSpecialInvestigate as true for all wikis is no longer needed and thus can be removed from mediawiki configuration.

It may be desired to remove wgCheckUserEnableSpecialInvestigate in the future (as it would no longer be needed), so removing this config makes that possible with less steps.

The removal of this value from the config should wait until at least the next train is successfully concluded, in case the train is reverted.