dwrv_chest10 contains a key used in a vanilla FG quest, and is already on the validator's uniques list for that reason

A handful of cells in Mainland currently still use it though:
Aanthirin Region (4, -31)
Archtumz
Bthalag-Zturamz, Halls
Bthzundcheft, Hall of Towers
Namartyon
Nchulegfth, Hall of Bthuchend