remove combined {models,sprites}.mat, remove extra .mdl .spr exts

valve/pbr/models/rpgrocket.mdl/rpgrocket.mat

@@ -0,0 +1,16 @@
+
+{
+"for" "#models/rpgrocket/rocket.mdl"
+//"basecolor_map" "rocket.png"
+//"normal_map" "rocket_normal.png"
+//"metal_map" "rocket_metal.png"
+//"roughness_map" "rocket_roughness.png"
+}
+
+{
+"for" "#models/rpgrocket/rocketmotor.mdl"
+//"basecolor_map" "rocketmotor.png"
+//"normal_map" "rocketmotor_normal.png"
+//"metal_map" "rocketmotor_metal.png"
+//"roughness_map" "rocketmotor_roughness.png"
+}