Get rid of Reflection hack used to override factory member
This caused some difficult to reproduce test failures when
WikibaseRepo::getSnakFormatterFactory() was called before the caching
PropertyDataTypeLookup was overwritten.
Bug: T200693
Bug: T201141
Bug: T197771
Change-Id: I2c03c4bcac41bdf9801a85aabbf84ce7b46138b7