Remove unused structures from lighting fragment shaders (#3497)

examples/shaders/resources/shaders/glsl100/lighting.fs

@@ -18,12 +18,6 @@ uniform vec4 colDiffuse;
 #define     LIGHT_DIRECTIONAL       0
 #define     LIGHT_POINT             1
 
-struct MaterialProperty {
-    vec3 color;
-    int useSampler;
-    sampler2D sampler;
-};
-
 struct Light {
     int enabled;
     int type;

examples/shaders/resources/shaders/glsl120/lighting.fs

@@ -16,12 +16,6 @@ uniform vec4 colDiffuse;
 #define     LIGHT_DIRECTIONAL       0
 #define     LIGHT_POINT             1
 
-struct MaterialProperty {
-    vec3 color;
-    int useSampler;
-    sampler2D sampler;
-};
-
 struct Light {
     int enabled;
     int type;

examples/shaders/resources/shaders/glsl330/lighting.fs

@@ -19,12 +19,6 @@ out vec4 finalColor;
 #define     LIGHT_DIRECTIONAL       0
 #define     LIGHT_POINT             1
 
-struct MaterialProperty {
-    vec3 color;
-    int useSampler;
-    sampler2D sampler;
-};
-
 struct Light {
     int enabled;
     int type;