eavs_3d: Avoid enum check for < 0

eavs_3d: Avoid enum check for < 0

Evas_3D_Mesh_Primitive is a enum starting from 0 so it never will be below 0.
Just as the compiler tells us. Remove unneeded check.
lib/evas/canvas/evas_3d_primitive.c:48:4: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]