FIRE-34189 - Fix for Vignette behaviour is wrong.

FIX remove unwanted screen_res divisor
The vertex shader already normalises the vary_fragcoord to be (0..1)

indra/newview/app_settings/shaders/class1/post/exoVignetteF.glsl

@@ -18,7 +18,7 @@ in vec2 vary_fragcoord;
 void main ()
 {
     vec4 diff = texture(diffuseRect, vary_fragcoord.xy);
-    vec2 tc = vary_fragcoord / screen_res - 0.5f;
+    vec2 tc = vary_fragcoord - 0.5f;
     float vignette_val = 1 - dot(tc, tc);
     diff.rgb *= clamp(pow(mix(1, vignette_val * vignette_val * vignette_val * vignette_val * vignette.z, vignette.x), vignette.y), 0, 1);
     frag_color = diff;