[Therion] Remove symbols from legend

Can p_u_foo be hidden from the legend?

Some examples. Statements need to be in thconfig outside of layouts. #symbols removed from legends text en "point u:foo" "" text en "point station:temporary" "" text en "line wall:bedrock" "" text fr "line wall:bedrock" "" text mi "line wall:bedrock" "" text en "line border:visible" "" text en "line border:temporary" "" text en "line border:presumed" "" text en "line rock-edge" "" text en "area bedrock" "" text en "point stalactites" "" text en "point stalagmites" "" Bruce