SSAO: Small tweaks

- UV clamping on depth sampling.
- Removed unused functions.

Assets/ScriptableRenderPipeline/HDRenderPipeline/Lighting/AmbientOcclusion/Resources/CommonAmbientOcclusion.hlsl

 // A small value used for avoiding self-occlusion.
 static const float kEpsilon = 1e-6;
 
-float2 SinCos(float theta)
-{
-    float sn, cs;
-    sincos(theta, sn, cs);
-    return float2(sn, cs);
-}
-
-// Pseudo random number generator with 2D coordinates
-float UVRandom(float u, float v)
-{
-    float f = dot(float2(12.9898, 78.233), float2(u, v));
-    return frac(43758.5453 * sin(f));
-}
-
 // Interleaved gradient function from Jimenez 2014 http://goo.gl/eomGso
 float GradientNoise(float2 uv)
 {

Assets/ScriptableRenderPipeline/HDRenderPipeline/Lighting/AmbientOcclusion/Resources/Estimation.hlsl

         // Project the sample point and get the view-space position.
         float2 spos_s1 = float2(dot(unity_CameraProjection[0].xyz, vpos_s1),
                                 dot(unity_CameraProjection[1].xyz, vpos_s1));
-        float2 uv_s1_01 = (spos_s1 / vpos_s1.z + 1.0) * 0.5;
+        float2 uv_s1_01 = saturate((spos_s1 / vpos_s1.z + 1.0) * 0.5);
         float depth_s1_raw = LOAD_TEXTURE2D(_MainDepthTexture, uint2(uv_s1_01 * _ScreenSize.xy)).x;
         float3 vpos_s2 = ComputeViewSpacePosition(uv_s1_01, depth_s1_raw, _InvProjMatrix);