If you go into the XML folder under CustomAssets, you'll see subfolders for Art, Civilizations, Units, etc.
The ones you need to delete are CIV4CivilizationInfos.xml and CIV4LeaderHeadInfos.xml under 'civilizations', and CIV4UnitClassInfos.xml and CIV4UnitInfos.xml under 'units'. Those are the only ones that really matter.
Under 'text', there are 4 files - _Civilopedia_CivLeaders, _Civilopedia_Units, _Strategy, and _Objects.
Under 'art', there are 3 files - _Civilization, _Leaderhead, and _Unit.
Under 'interface' there are 2 files - _ColorVals and _PlayerColorInfos
The ones you need to delete are CIV4CivilizationInfos.xml and CIV4LeaderHeadInfos.xml under 'civilizations', and CIV4UnitClassInfos.xml and CIV4UnitInfos.xml under 'units'. Those are the only ones that really matter.
Under 'text', there are 4 files - _Civilopedia_CivLeaders, _Civilopedia_Units, _Strategy, and _Objects.
Under 'art', there are 3 files - _Civilization, _Leaderhead, and _Unit.
Under 'interface' there are 2 files - _ColorVals and _PlayerColorInfos